DETECTION OF CRANKCASE INTEGRITY VULNERABILITY

Abstract

A method for an engine crankcase ventilation system comprising: when starting an engine (10) - reducing an opening of a PCV valve (78) to a low-flow position, wherein the PCV valve (78) is coupled in a PCV line (76) between an intake manifold (15) and a crankcase (28), the intake manifold (15) being arranged downstream of a throttle (44), - distinguishing a disconnection of a crankcase ventilation tube (74) from a deterioration of the PCV valve (78) based on characteristics of a temporary drop in crankcase ventilation tube pressure, - Setting a diagnostic code based on whether the crankcase ventilation tube (74) is disconnected or whether the PCV valve (78) is impaired, wherein a first side (101) of the crankcase ventilation tube (74) is coupled to a fresh air intake duct (13) upstream of a compressor (50) and a second side (102) of the crankcase ventilation tube (74) is coupled to the crankcase (28).

Description

Engines may include crankcase ventilation systems to vent gases from the crankcase and into an engine intake manifold to ensure continuous exhaust of gases from the interior of the crankcase to reduce degradation of various engine components in the crankcase. The positive crankcase ventilation ("PCV") system may include a positive crankcase ventilation (PCV) valve to enable a one-way flow of crankcase gases from within the crankcase to the intake manifold.Positive positive crankcase ventilation systems (also referred to as a positive crankcase ventilation system below) may be diagnosed intermittently for PCV valve degradation. An exemplary approach for PCV valve diagnostics is shown by Sa tour in US 2009 / 0 211 545 A1. Therein, PCV valve degradation is determined based on air changes (e.g., changes in throttle position) and fuel changes (e.g., fuel injection changes) required to maintain an idle speed in adjusting an opening of the PCV valve. The opening of the PCV valve is again selected based on an air-fuel ratio of blow-by gas.The inventors have recognized potential issues with such approaches. For example, the blow-through based approach may result in a large noise problem due to different engine loads. These include, for example, engine friction, air pressure, refrigerant compressor load, alternator load, etc. Consequently, computationally intensive noise mitigation algorithms may be required.US 2010 / 0 147 270 A1 describes a method with which it is possible to determine whether a crankcase of an engine has a fracture point. For this purpose, a pressure in the crankcase is evaluated. The document U.S. Pat. No. 6,575,022 B1 relates to a blow-by sensor for a crankcase. The document U.S. Pat. No. 5,792,949 A relates to a system for monitoring a ventilation system of a crankcase. The publication US 2009 / 0 183 706 A1 describes a method for starting an engine which can detect anomalies in the valve control.The document U.S. Pat. No. 4,102,314 A concerns how a crankcase can be ventilated without the driving properties being impaired. The publication US 2006 / 0 276 952 A1 relates to a method for controlling an internal combustion engine of a vehicle, wherein a torque requested by the driver is analyzed. The document DE 100 26 492 A1 describes a method for the functional diagnosis of a venting system in a crankcase of an internal combustion engine. The publication US 2006 / 0 149 434 A1 provides a method and a system for vehicle diagnosis.In the publication US 2010 / 0 180 872 A1, a system for checking dirt in an engine is presented. U.S. Pat. No. 2,516,547 A relates to a ventilation system for a crankcase. The publication US 2001 / 0 022 175 A1 relates to a combined system for ventilating a crankcase and a cylinder. US 5 897 597 A describes a system for diagnosing faults in crankcase ventilation systems. The document DE 10 2010 029 150 A1 relates to a variable ventrinozzle system and method for a motor.It is an object of the invention to provide an improved method for an engine crankcase ventilation system, an improved method for an engine and an improved engine crankcase ventilation system. The object is achieved by the engine crankcase ventilation system according to claim 1, the method for an engine according to claim 9 and the engine crankcase ventilation system according to claim 16.In one approach, a method for an engine crankcase ventilation system is provided to at least partially address these issues. The method includes: indicating degradation of a valve coupled between a crankcase and an intake manifold based on characteristics of a transient drop in crankcase vent tube pressure at engine cranking. In this way, devices may be used to diagnose PCV valve degradation.In one example, a crankcase ventilation system may include a crankcase ventilation tube coupled between an air intake passage and a crankcase. A pressure sensor (or flow sensor) may be disposed within the crankcase ventilation tube to provide an estimate of the flow or pressure of the air flowing through the ventilation tube. At engine start-up, an estimated crankcase vent tube pressure profile may be compared to an expected crankcase vent tube pressure profile. In particular, during engine cranking and cranking, when manifold vacuum is low when the PCV valve is operating properly, a flow rate through the crankcase vent tube may be expected to increase because engine speed is increased by cranking and cranking and the PCV valve is initially in the lowest throttle position. When the manifold vacuum reaches a threshold, the flow rate through the vent tube may be expected to decrease and stabilize. This may be reflected as a transient drop in crankcase vent tube pressure at engine cranking. Thus, based on the estimated crankcase vent tube pressure profile not corresponding to the expected crankcase vent tube pressure profile, a controller may determine that the PCV is degraded. For example, based on an amplitude of the transient drop in crankcase vent tube pressure being less than the expected amplitude (or threshold), it may be determined that the PCV valve is stuck closed (or is in a low flow position). As another example, based on the magnitude of the transient drop in crankcase vent tube pressure being greater than the expected magnitude (or threshold), it may be determined that the PCV valve is stuck open (or is in a high flow position).In this way, by correlating changes in crankcase ventilation air flow and PCV valve position, PCV valve degradation may be reliably detected. By using the existing crankcase ventilation system pressure sensor to identify PCV valve degradation, the need for additional sensors as well as computationally intensive noise mitigation algorithms is reduced, thereby offering cost and complexity reduction advantages without reducing the accuracy of degradation. Further, the approach allows the crankcase ventilation system to remain active during a diagnostic procedure.It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not intended to identify key or essential features of the claimed subject matter, the scope of which is clearly defined by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that solve any disadvantages identified above or in any part of this disclosure. FIG. 1 is a partial engine view according to the disclosure. FIGS. 2A-B show a high level flow chart for indicating degradation of one or more constituents of a crankcase ventilation system based on changes in crankcase ventilation tube pressure during cranking and / or engine running. FIGS. 3-4 show example methods for indicating crankcase ventilation system injury based on a transient drop in crankcase vent tube pressure during cranking and changes in crankcase vent tube pressure relative to changes in manifold air flow during engine running. FIG. 5 shows an example method for indicating degradation of a PCV valve based on changes in crankcase vent tube air flow during low manifold air flow conditions. FIG. 6 shows an example method for indicating a blockage of an air intake filter based on output of a pressure sensor disposed in the crankcase vent tube. FIGS. 7 through 8 show example changes in crankcase vent tube pressure that may be used to indicate a crankcase injury and identify a position of the injury. FIG. 9 shows example methods for indicating air filter plugging based on changes in crankcase vent tube pressure relative to changing manifold air flow. FIG. 10 shows example changes in crankcase vent tube pressure that may be used to indicate degradation of a PCV valve.The following description relates to systems and methods for monitoring crankcase ventilation system integrity in an engine crankcase ventilation system, such as the system of FIG. 1. An engine controller may be configured to execute various routines, such as the routines of FIGS. 2A-B and 3-6, to indicate crankcase ventilation system degradation based on changes in crankcase ventilation tube pressure (or air flow) during engine cranking, as well as changes in crankcase ventilation tube pressure relative to changes in manifold air flow during engine running. The crankcase vent tube pressure sensor may be configured to indicate static pressure or dynamic pressure. Further, it may be disposed in a venturi (a necked down portion of the vent tube) and thus sensitive to either pressure or flow rate, or both. For example, the controller may determine a damage to the crankcase system based on characteristics of a transient drop in crankcase vent tube pressure and then further identify a position and origin of the damage based on both the transient drop and changes in crankcase vent tube negative pressure during engine running (FIGS. 3, 4, 7, and 8). As another example, the controller may determine degradation of a PCV valve based on deviations of an expected crankcase vent tube pressure / air flow profile relative to an actual pressure / air flow profile (FIGS. 5 and 10 ). Additionally, based on deviations of a vent tube pressure level from a reference pressure during high manifold air flow conditions, the controller may detect air filter plugging (or intake hose collapse) learning the reference pressure (and associated offset) during low manifold air flow conditions (FIGS. 6 and 9 ). By using the same sensor to identify degradation in different system components, device reduction advantages are achieved without compromising sensing accuracy.Referring now to FIG. 1, it shows an example system configuration of a multi-cylinder internal combustion engine, generally depicted at 10, which may be included in a propulsion system of a motor vehicle. The engine 10 may be controlled at least in part by a control system including a controller 12 and by input from a vehicle operator 130 via an input device 132. In this example, the input device 132 includes an accelerator pedal and a pedal position sensor 134 for generating a proportional pedal position signal PP.The engine 10 may include a lower portion of the engine block, generally indicated at 26, including a crankcase 28 enclosing a crankshaft 30, with an oil pan 32 disposed below the crankshaft. An oil fill passage 29 may be disposed in the crankcase 28 such that oil may be supplied to the oil pan 32. The oil filling passage 29 may include an oil cap 33 to seal the oil passage 29 when the engine is operating. A level bar tube 37 may also be disposed in the crankcase 28 and may include a level bar 35 for measuring an oil level in the oil pan 32. Additionally, the crankcase 28 may include several other openings for servicing components in the crankcase 28. These openings in the crankcase 28 may be maintained closed during engine operation so that a crankcase ventilation system (described below) may operate during engine operation.The upper portion of the engine block 26 may include a combustion chamber (i.e., a cylinder) 34. The combustion chamber 34 may include combustion chamber walls 36 with a piston 38 disposed therein. The piston 38 may be coupled to the crankshaft 30 such that reciprocating motion of the piston is translated into rotational motion of the crankshaft. Combustion chamber 34 may receive fuel from a fuel injector 45 (configured herein as a direct fuel injector) and intake air from an intake manifold 42 disposed downstream of a throttle 44. The engine block 26 may also include an engine coolant temperature (ECT) sensor 46 that inputs to an engine controller 12 (described in more detail below).A throttle 44 may be disposed in the engine intake to control the flow of air entering the intake manifold 42 and may be preceded upstream by a compressor 50, for example followed by a charge air cooler 52. an air filter 54 may be disposed upstream of the compressor 50 and may filter fresh air entering an intake passage 13. Intake air may enter combustion chamber 34 via cam-actuated intake valve system 40. In the same way, burnt exhaust gas may exit the combustion chamber 34 via a cam-actuated exhaust valve system 41. In an alternative embodiment, one or more of the intake valve system and the exhaust valve system may be electrically actuated.Combustion exhaust gases exit the combustion chamber 34 via an exhaust passage 60 disposed upstream of a turbine 62. An exhaust gas sensor 64 may be disposed upstream of the turbine 62 along the exhaust passage 60. The turbine 62 may be equipped with a wastegate (not shown) that bypasses it. The sensor 64 may be a suitable sensor for providing an indication of exhaust gas air-fuel ratio, such as a linear oxygen sensor or universal or opposed exhaust gas oxygen (UEGO), a two-state oxygen sensor or EGO, a heated EGO (HEGO), a NO x-, HC, or CO sensor. Exhaust gas sensors 64 may be connected to controller 12.In the example of FIG. 1, a positive crankcase ventilation (PCV) system 16 is coupled to the engine intake so that gases in the crankcase may be vented from the crankcase in a controlled manner. During non-boosted conditions (when manifold pressure (MAP) is less than barometric pressure (BP)), crankcase ventilation system 16 draws air into crankcase 28 via a vent hole or crankcase vent tube 74. a first side 101 of crankcase vent tube 74 may be mechanically coupled or connected to fresh air intake passage 13 upstream of compressor 50. In some examples, the first side 101 of the crankcase ventilation tube 74 (as shown) may be coupled to the intake passage 13 downstream of the air filter 54. In other examples, the crankcase ventilation tube may be coupled to the intake passage 13 upstream of the air filter 54. A second, opposite side 102 of the crankcase ventilation tube 74 may be mechanically coupled or connected to the crankcase 28 via an oil separator 81.The crankcase vent tube 74 further includes a sensor 77 coupled therein to provide an estimate of the air flowing through the crankcase vent tube 74 (e.g., flow rate, pressure, etc.). In one embodiment, crankcase vent tube sensor 77 may be a pressure sensor. When configured as a pressure sensor, the sensor 77 may be an absolute pressure sensor or a relative sensor. In an alternative embodiment, sensor 77 may be a flow sensor or flowmeter. In yet another embodiment, sensor 77 may be configured as a venturi. In some embodiments, the crankcase vent tube may optionally include a venturi 75 for sensing flow therethrough, in addition to a pressure or flow sensor 77. In still other embodiments, pressure sensor 77 may be coupled to a throat of a venturi 75 to estimate a pressure decrease across the venturi. One or more additional pressure and / or flow sensors may be coupled to the crankcase ventilation system at changing positions. For example, a barometric pressure sensor (BP sensor) 57 may be coupled to intake passage 13 upstream of air filter 54 to provide an estimate of barometric pressure. In an example where crankcase vent tube sensor 77 is configured as a relative sensor, BP sensor 57 may be used in conjunction with relative pressure sensor 77. In some embodiments, a pressure sensor (not shown) may be coupled into the intake passage 13 downstream of the air filter 54 and upstream of the compressor 50 to provide an estimate of the compressor inlet pressure (CIP). However, because crankcase vent tube pressure sensor 77 may provide an accurate estimate of compressor inlet pressure during conditions of increased engine air flow (such as during engine run-up), the need for a dedicated CIP sensor may be reduced. Additionally, a pressure sensor 59 may be coupled downstream of the compressor 50 to provide an estimate of throttle inlet pressure (TIP). Any of the above-mentioned pressure sensors may be absolute pressure sensors or relative sensors.The PCV system 16 also vents gases from the crankcase and into the intake manifold 42 via a conduit 76 (also referred to herein as PCV conduit 76). In some examples, the PCV conduit 76 may include a one-way PCV valve 78 (i.e., a passive valve that tends to seal when flow is in the opposite direction) to ensure continuous purging of crankcase gases from the interior of the crankcase 28 before being connected to the intake manifold 42. In one embodiment, the PCV valve may change its flow restriction in response to the pressure decrease across it (or the flow rate through it). However, in other examples, conduit 76 may not include a one-way PCV valve. In still other examples, the PCV valve may be an electronically controlled valve controlled by controller 12. It will be appreciated that PCV flow, as used herein, refers to the flow of gases through the conduit 76 from the crankcase to the intake manifold. Similarly, PCV reflux refers to the flow of gases through the conduit 76 from the intake manifold to the crankcase. PCV reflux may occur when intake manifold pressure is higher than crankcase pressure (i.e., during boosted engine operation). In some examples, the PCV system 16 may be equipped with a check valve to prevent PCV backflow. It will be appreciated that while the depicted example shows the PCV valve 78 as a passive valve, this is not to be understood as limiting, and in alternative embodiments, the PCV valve 78 may be an electronically controlled valve (e.g., a powertrain control module (PCM) controlled valve), wherein a controller may command a signal to change a position of the valve from an open position (or a high flow position) to a closed position (or a low flow position), or vice versa, or any position therebetween.The gases in the crankcase 28 may be unburned fuel, unburned air, and fully or partially combusted gases. Furthermore, a lubricant mist may also be present. Thus, various oil separators may be included in the crankcase ventilation system 16 to reduce oil mist leakage from the crankcase through the PCV system. For example, the PCV conduit 76 may include a unidirectional oil separator 80 that filters oil from vapors exiting the crankcase 28 before entering the intake manifold 42. Another oil separator 81 may be disposed in the conduit 74 to remove oil from the flow of gases exiting the crankcases during boosted operation. Additionally, the PCV conduit 76 may also include a negative pressure sensor 82 coupled to the PCV system. In other embodiments, a MAP or manifold vacuum (ManVac) sensor may be disposed in the intake manifold 42.The present inventors have recognized that by disposing the pressure sensor 77 in the crankcase vent tube 74, damage to the integrity of the crankcase system may be detected not only in high engine air flow conditions but also in low engine air flow conditions based on drawing down the vacuum in the vent tube. At the same time, crankcase vent tube pressure sensor 77 may also detect crankcase pulsations. This allows crankcase system degradation to be more accurately identified, while also allowing a position of crankcase system injury to be reliably determined. As such, because the pressure sensor in the vent tube is used to conclude or estimate the presence of airflow through the vent tube, the pressure sensor can also be used (or exchanged with) a flowmeter or meter. Thus, in some embodiments, damage to the crankcase system may also be identified using a flowmeter or venturi in the crankcase vent tube. Since flow through the crankcase vent tube is also affected by the opening / closing of the PCV valve 78, the same crankcase vent tube sensor may also be advantageously used to diagnose degradation of the PCV valve. Moreover, because the crankcase ventilation pressure sensor will sense compressor inlet pressure during engine running conditions when engine airflow is increased, the need for a CIP sensor may be reduced. In addition, since the flow through the crankcase vent tube is also affected by the clogging state of the air cleaner 54, the same crankcase vent tube sensor can be advantageously used also for the diagnosis of filter clogging. In this way, through the use of an existing crankcase vent tube pressure or pressure can be controlled.Further, for example, air flow sensor of an engine system for diagnosing various engine components, such as a PCV valve, an intake air filter, as well as for diagnosing damage to the crankcase ventilation system, advantages of hardware and software reduction in the engine system may be achieved.Controller 12 is shown in FIG. 1 as a microcomputer including microprocessor unit 108, input / output ports 110, an electronic storage medium for executable programs and calibration values, shown as read only memory chip 112 in this particular example, random access memory 114, battery powered memory 116, and a data bus. Controller 12 may receive various signals from sensors coupled to engine 10, including measurement of inducted mass air flow (MAF) from mass air flow sensor 58, engine coolant temperature (ECT) from temperature sensor 46, PCV pressure from vacuum sensor 82, exhaust air-fuel ratio from exhaust gas sensor 64, crankcase ventilation pressure sensor 77, BP sensor 57, CIP sensor 58, TIP sensor 59, etc. Further, controller 12 may monitor and adjust the position of various actuators based on input received from the various sensors. These actuators may include, for example, the throttle 44, the intake and exhaust valve systems 40, 41, and the PCV valve 78. Storage medium read-only memory 112 may be programmed with computer readable data representing instructions executable by processor 108 to perform the methods described below as well as other variations that are contemplated but not specifically listed. Example methods and routines are described herein with reference to FIGS. 2A-6.In this way, the system of FIG. 1 enables various methods for diagnosing engine components coupled to a crankcase ventilation system based on at least one estimated crankcase ventilation tube pressure. In one embodiment, a method is enabled for an engine, comprising indicating crankcase ventilation system degradation based on characteristics of a transient drop in crankcase ventilation tube pressure during engine cranking. In another embodiment, an engine method is enabled that includes indicating a position of a damage to the crankcase ventilation system based on both a transient drop in crankcase ventilation tube pressure during cranking and a change in crankcase ventilation tube pressure during continuous state engine airflow. In yet another embodiment, an engine method is enabled that includes, during engine cranking while manifold air flow is less than a threshold, increasing throttle opening and indicating crankcase ventilation system degradation based on a change in crankcase ventilation tube pressure subsequent to the throttle opening. In yet another embodiment, a method for an engine is enabled, comprising indicating degradation of the intake air filter based on a pressure sensor in a crankcase ventilation tube. In another embodiment, a method is enabled for an engine that enables indicating degradation of a valve coupled between a crankcase and an intake manifold based on characteristics of a transient drop in crankcase vent tube pressure during engine cranking.Turning now to FIGS. 2A-B, a method 200 is shown for indicating degradation of one or more engine components, including crankcase ventilation system components and intake air filters, based on changes in crankcase ventilation pressure (or air flow) during engine launch and run. By using the same sensor to detect degradation in multiple engine components, cost and component reduction advantages are achieved.At 202, an engine start from rest may be confirmed. For example, it can be confirmed that the engine has been completely stopped for a period of time and the engine is started from the state of being completely stopped. After confirmation, at 204, the engine may be started by cranking the engine with the assistance of a cranking engine. Next, at 206, it may be determined if intake manifold vacuum is higher than a threshold. If not, at 208, an actuator may be adjusted to increase intake manifold vacuum to the threshold. In one example, the actuator being adjusted may be an intake throttle, wherein the adjusting includes increasing an opening of the throttle. In another example, the actuator being adjusted may be a PCV valve coupled between the crankcase and the intake manifold, wherein the adjusting includes opening the PCV valve (if the valve is a switching valve) or increasing an opening of the PCV valve (if the valve is a switching ratio controlled valve).As such, the PCV valve may be responsive to both its pressure decrease and the flow rate of air therethrough. Specifically, when in a low throttle position, the flow rate through the crankcase ventilation tube (CVT) is high. In comparison, when in the high throttle position (sound limited volumetric flow), the flow rate through the CVT is fixed (neglecting the relatively small blow-through component at high ManVac). When the manifold vacuum becomes substantially sufficient to drive flow (e.g., 5 kPa) but not high enough to begin causing throttling in the PCV valve (e.g., 25 kPa), a very high CVT flow rate occurs. This high flow rate is seen as a pressure drop in the CVT pressure sensor. The presence of this drop confirms proper PCV operation and the absence of a crankcase injury.Once the intake manifold vacuum is at the threshold, from 206 to 208, the routine proceeds to 210 where, while the engine is cranking and while the vacuum is maintained at or above the threshold vacuum level, a crankcase vent tube pressure (and / or airflow) is monitored. This includes monitoring an output of the crankcase vent tube pressure sensor during engine cranking while engine speed is below a threshold speed and before fuel is injected into any cylinder.As such, during engine cranking, intake manifold vacuum may be low such that the position of the PCV valve of the crankcase ventilation system is open (e.g., the PCV valve may be maximally open or at a position of maximum effective area). This causes a large air flow to be drawn into the intake manifold through the intake air filter, then through the crankcase vent tube, then through the crankcase. This flow through the crankcase vent tube to the intake manifold may be detected by a flowmeter or venturi as a transient increase in airflow at the crankcase vent tube or by a pressure sensor as a transient decrease in crankcase vent tube pressure (or a transient increase in crankcase vent tube vacuum). As engine speed increases subsequent to cranking and manifold vacuum increases, air flow through the crankcase vent tube into the intake manifold may decrease. Thus, at 212, the routine includes estimating properties of a transient drop in crankcase vent tube pressure during cranking. The estimated characteristics include, for example, a transient decay amplitude, a decay time (e.g., relative to engine speed or piston position), a decay duration, etc.Next, at 214, the routine includes determining and indicating crankcase ventilation system degradation based on one or more characteristics of the transient drop in crankcase ventilation pressure during engine launch. As discussed above, during engine cranking, when manifold vacuum is lower, an increased air flow from the air filter through the crankcase vent tube to the intake manifold is seen as a transient drop in crankcase vent tube pressure (or a transient increase in vent tube vacuum or air flow). However, this transient droop may be affected by the presence of a damage to the crankcase system (e.g., if the vent tube is disconnected) as well as the position of the PCV valve (e.g., the PCV valve is stuck open or stuck closed). Thus, as detailed with FIGS. 3-4, based on at least an amplitude of the transient drop in crankcase vent tube pressure, a damage to crankcase ventilation system integrity as well as a position of the damage may be indicated. For example, in response to the transient droop amplitude being less than a threshold during cranking, a fault in the crankcase system may be detected.Following sensing crankcase system injury, the routine proceeds to 216, where PCV valve degradation is determined based on transient pressure change characteristics at the crankcase vent tube. As further detailed at FIG. 5, this includes indicating degradation of the PCV valve based on an estimated profile of crankcase vent tube pressure that deviates from an expected profile during engine cranking. It will be appreciated that while the routine shows degradation of the PCV valve being detected after a crankcase system fault is diagnosed, in alternative embodiments, the diagnoses may be performed in parallel.After diagnosing a crankcase system fault and a PCV valve degradation during engine cranking, at 218, the routine includes injecting fuel to engine cylinders and initiating a first cylinder combustion event. During engine cranking, intake manifold air flow may be lower, and as engine speed (e.g., increases to an idle speed), intake manifold air flow may gradually increase. Thereafter, the controller may continue the cylinder combustion events to enable engine cranking. At 220, it may be confirmed that intake manifold air flow (or engine intake air flow) is higher than a threshold air flow. As such, once the engine is at or above an idle speed, the manifold air flow rate as well as crankcase vent tube pressure may be at steady state levels. Specifically, engine speed (along with throttle position) affects intake manifold pump-out characteristic during cranking and cranking, thereby affecting PCV valve position.At 222, the routine includes monitoring steady state manifold air flow and steady state crankcase vent tube pressure. Thereafter, at 224 and 226, the routine includes determining a crankcase ventilation system degradation and an intake air filter degradation based on the estimated change in crankcase ventilation tube pressure under steady state conditions. As further detailed in FIGS. 3-4, at 224, this includes indicating crankcase system degradation based on a change (e.g., a decrease) in steady state crankcase vent tube pressure relative to a change (e.g., an increase) in steady state manifold air flow during engine operation. As further detailed in FIG. 5, indicating degradation of the air filter at 226 includes indicating a degree of air filter plugging based on a rate of change (e.g., a rate of decrease) in crankcase vent tube pressure in the steady state during engine running. As detailed herein, air filter plugging / hose collapse detection is performed during engine running because the diagnostic has higher sensitivity at higher engine air flow rates. It will be appreciated that while the routine shows that degradation of the air filter is determined in parallel with diagnosing damage to the crankcase system, in alternative embodiments, the diagnoses may be performed sequentially.At 228, after all diagnostic routines have been performed, one or more diagnostic codes may be set to indicate degradation of the subject engine component. As such, different diagnostic codes may be set to indicate air filter plugging, crankcase system injury (including different codes to indicate the position / condition of the injury), and PCV valve degradation. At 230, the routine includes performing a remedial action based on the display and the diagnostic code that was set.In one example, the controller may also record a number of detections of crankcase injuries to determine if a threshold number of damage detections has been reached. For example, the diagnostic routines of FIGS. 2A-B may be repeated multiple times during a given engine operation, including being repeated continuously from key-on to key-off, as well as during key-off. If the routine indicates a crankcase violation, the controller may record any event of a violation detection for that engine operating duration and execute a notification routine once a threshold number of detections has been reached. The threshold may be injury detection in some embodiments. In other embodiments, to avoid false positive tests, the threshold may be multiple injury detections, such as two, five, ten, etc. Once the threshold number of injury detections is reached, a message may be displayed to the vehicle operator, such as by activating a malfunction indication light (MIL) to notify the operator of the vehicle of the detected crankcase injury. In addition, the operator may be prompted to check for possible injury positions (e.g., a loose or missing oil cap or by an misaligned / loose level stick). Alternatively, the likely position of an injury (as determined in FIG. 4, detailed below) may be displayed.The remedial actions may also include adjusting one or more operating parameters to prevent additional engine damage during engine operation with a damaged crankcase, PCV valve, or clogged filter. For example, the remedial actions may include acting to delay draining lubricant from the crankcase if it is indicated that the crankcase is injured. Other example remedial actions include reducing intake of air into the engine, limiting a speed or torque of the engine, limiting a fuel injection amount supplied to the engine, limiting a throttle opening, limiting an amount of boost, shutting down the turbocharger, and / or various other actions intended to limit intake of engine lubricant from the injured crankcase. In some embodiments, the remedial action taken may be one of a plurality of remedial actions taken when a crankcase injury is detected. As yet another example, the plurality of auxiliary actions may include adding lubricant to the crankcase or pumping lubricant from a sub reservoir and into the crankcase.In one example, responsive to the crankcase vent tube being disconnected, boosted engine operation (i.e., where MAP>BP) may be limited or discontinued. In another example, in response to an oil cap releasing or an oil level rod disengaging, an engine speed may be limited. By limiting engine speed, oil spin can be reduced because at high engine speeds spin oil is more likely to leak over the oil cap / level rod than at low engine speeds. As yet another example, in response to a PVC valve stuck closed, no fault mode action may be performed because the blow-by gas (and any entrained oil mist) is simply directed to the compressor inlet and then burned. In an alternative example, a controller may limit engine speed by a greater amount responsive to the indication that the crankcase vent tube is disconnected, while limiting engine speed by a lesser amount responsive to the indication of PCV valve degradation.Turning now to FIG. 3, a method 300 is shown for indicating crankcase ventilation system degradation based on transient crankcase ventilation tube pressure characteristics during engine cranking. The method further enables crankcase ventilation system degradation to be determined based on a change in crankcase vent tube pressure relative to a change in manifold air flow during engine running conditions.The routine of FIG. 3 operates on the principle that if the droop occurs (i.e., if there is a high CVT flow while a PCV valve is in a low throttle position), then the integrity of the PCV system may be confirmed (except for a first side separation 101). Separation at the first side 101 can be easily detected in vehicles equipped with a MAF sensor. For vehicles without MAF sensors, the separation at the first side 101 is detectable by the absence of a high engine airflow pressure decrease at the MAF sensor 58 or the CVT pressure sensor 77.At 302, the routine includes estimating a crankcase vent tube pressure during engine cranking and monitoring a transient drop in crankcase vent tube pressure during engine cranking. The crankcase vent tube pressure may be estimated or inferred by one of a pressure sensor, a flow sensor, or a venturi coupled into the crankcase vent tube. As used herein, estimating crankcase vent tube pressure includes during engine cranking prior to a first combustion event from rest, i.e., prior to fuel injection to any engine cylinder. When the flow rate through the CVT is low, the CVT pressure sensor is basically a static pressure sensor. It detects both the continuous flow pressure decrease due to the flow through the air filter and the crankcase pressure pulsations. Pipe separations and crankcase injuries affect pulsation amplitude. At 304, a transient decay amplitude may be determined and compared relative to a threshold amplitude. In one example, the threshold amplitude may be based on manifold vacuum during engine cranking. Herein, the threshold may be increased as the expected flow through the PCV valve changes. That is, under some conditions, the threshold amplitude may increase with increasing manifold vacuum, and under other conditions, the threshold amplitude may decrease with increasing manifold vacuum.If the transient decay amplitude is less than the threshold, then at 314, the routine determines and indicates crankcase ventilation system degradation. That is, in response to insufficient air flow through the crankcase vent tube during cranking, a system violation may be detected. Indicating degradation of the crankcase ventilation system includes indicating that the crankcase ventilation tube is disconnected. For example, the crankcase vent tube may have been separated at a first side where the vent tube is mechanically coupled to the air intake passage (upstream of a compressor) or at a second, opposite side where the vent tube is mechanically coupled to the engine crankcase via an oil separator. As detailed with FIG. 4, the controller may be configured to execute an additional routine to identify the position and condition of the injury (e.g., the position of the vent tube separation) based on both the transient drop in crankcase vent tube pressure during engine cranking (when engine air flow is lower) and a change in steady state crankcase vent tube pressure relative to a change in steady state manifold air flow during engine running conditions (when engine air flow is higher). In this way, a controller may indicate a disconnection of a crankcase vent tube from a crankcase ventilation system based on changes in airflow through the crankcase vent tube during engine cranking and engine running.Returning to 304, if the amplitude of the transient droop is not less than the threshold, it may be possible that there is no damage to the crankcase system. To confirm this, the routine proceeds to further determine a crankcase system violation during engine running conditions. Specifically, at 306, it may be confirmed that manifold vacuum is higher than a threshold. That is, it may be confirmed that the engine has crossed the engine cranking state and is operating at or above a defined engine speed (e.g., at or above an engine idle speed) as the engine airflow rate (inferred or measured) is higher. Upon confirming that the manifold air flow is higher than the threshold, at 308, the routine includes monitoring a change in steady state crankcase vent tube pressure relative to a change in steady state manifold air flow. Specifically, as the engine is running and engine speed increases, the manifold air flow may gradually increase in steady state. At the same time, in the absence of any injury, the crankcase vent tube pressure may be expected to gradually decrease (i.e., a level of vacuum generated in the crankcase vent tube may be increased due to an increased airflow through the crankcase vent tube).At 310, it may be determined if during engine operation, the decrease in steady state crankcase vent tube pressure (CVT) is proportional to the increase in steady state manifold air flow. That is, it may be determined if there is more than a threshold amount of vacuum generated at the crankcase vent tube during engine running at a high engine air flow rate. If during engine operation, the change in steady state crankcase vent tube pressure and steady state manifold air flow is proportional, then at 312, it may be determined that there is no degradation or violation of the crankcase ventilation system. If the change is not proportional, then the routine proceeds to 314 to indicate crankcase ventilation system degradation (e.g., the crankcase ventilation tube is disconnected) based on a decrease in crankcase ventilation tube pressure being not proportional to an increase in manifold air flow over a period of time while engine speed is at or above a threshold speed. For example, in response to reduced or no vacuum generation in the crankcase vent tube at higher engine air flows, a crankcase injury is detected. As used herein, determining whether during engine operation, the decrease in steady state crankcase vent tube pressure (CVT) is proportional to the increase in steady state manifold air flow may include determining whether its ratio deviates from a threshold ratio or whether its absolute difference is greater than a threshold difference.A controller may indicate the crankcase ventilation system violation by setting a diagnostic code at 314. Further, in response to the display, one or more remedial actions may be performed. These may include, for example, limiting an engine speed and load so as to reduce / delay lubricant depletion from the injured crankcase and lubricant aspiration from the crankcase into engine components. Example maps used to identify damage to the crankcase system are illustrated herein at FIGS. 7 through 8.Turning now to FIG. 4, method 400 illustrates a routine that may be executed to determine a position of crankcase system injury based on and after both a transient drop in crankcase vent tube pressure during engine cranking and a change in crankcase vent tube vacuum during engine cranking.At 402, it may be confirmed that the amplitude of the transient drop in crankcase vent tube pressure at cranking is less than a threshold. As detailed with FIG. 3, during engine cranking (in the absence of a fault), if engine air flow is lower, a higher air flow through the crankcase vent tube may be experienced, which is sensed by the crankcase vent tube pressure sensor as a transient drop in vent tube pressure (or a transient increase in vent tube negative pressure). If there is an injury, an amplitude of the transient decay may be reduced.After confirmation, at 404, it may be determined whether a ratio of the decrease in crankcase vent tube pressure (CVT) in steady state during engine operation (i.e., after engine cranking while engine speed is higher than a threshold) to the increase in manifold steady state air flow during engine operation is lower than a threshold ratio. Alternatively, it may be determined whether the absolute difference therebetween is greater than a threshold difference. Therefore, it may be determined if vacuum generation at the vent tube during higher engine air flows is at or above a threshold level.In yet another embodiment, if a transient droop is observed, it may be determined that the PCV system has not degraded and the controller may thereafter check for a disconnection at the first page 101. This can be done by searching for an erroneous MAF reading and a pressure decrease at the MAP sensor that is too small at high engine air flow rates. Alternatively, the separation at the first side may be identified based on a pressure decrease at the CVT pressure sensor 77 being too small at high engine air flow rates. The detection of pulsations at the CVT pressure sensor 77 may also be used.In response to the transient drop in crankcase vent tube pressure during cranking being less than a threshold amplitude and the decrease in steady state crankcase vent tube pressure during the increase in steady state manifold air flow during engine running being less than a threshold rate, at 406, a damage to the crankcase ventilation system at a first side of the crankcase vent tube may be detected. Further, in response to a damped transient drop in crankcase vent tube vacuum during engine cranking and substantially no crankcase vent tube vacuum (zero vacuum) being generated during engine ramp-up, it will be determined that crankcase ventilation system injury is due to the crankcase vent tube being separated on the first side where it is mechanically connected to an air intake passage. Example maps used to identify a damage to the crankcase system on the first side are illustrated herein at FIG. 7.In comparison, responsive to the transient drop in crankcase vent tube pressure during cranking being less than a threshold amplitude and the steady state decrease in crankcase vent tube pressure during the steady state increase in manifold airflow during engine running being greater than a threshold rate, at 408, a fault in the crankcase ventilation system at a second side of the crankcase vent tube may be detected. For example, in response to a damped transient drop in crankcase vent tube vacuum during engine cranking and a reduced crankcase vent tube vacuum being generated during engine cranking, a fault is detected on the second side of the vent tube. Specifically, it may be determined that there is a damage to the crankcase system at a second, opposite side of the crankcase vent tube where it is mechanically connected to the crankcase. As such, damage to the crankcase system at the second side may include one of a disconnection of the crankcase vent tube from the crankcase at the second side, a detachment of a crankcase oil fill port cap, a detachment of a crankcase oil level rod, and a blockage of the crankcase vent tube at the second side.To distinguish between the different injuries to the crankcase system on the second side, the routine then proceeds to 410 where an opening amount of the injury is determined. In one example, an opening size of the injury may also be determined. At 412, it may be determined if the opening amount is greater than a threshold amount. If yes, then at 414, based on the opening amount being greater than the threshold, a release of the crankcase oil fill port cover may be determined. Otherwise, at 416, it may be determined that the injury to the second side is due to a disconnection of the crankcase vent tube from the crankcase on the second side, detachment of the crankcase oil level rod, or blockage of the crankcase vent tube on the second side. Example maps used to identify a fault of the crankcase system on the second side are illustrated herein at FIGS. 7 through 8.As such, when the PCV valve is in the low throttle (fully open) position, large air flows normally result in the crankcase vent tube. The PCV valve may be in this position due to a default pneumatic controller, an active PCM controller, or a PCV valve fault. This high air flow rate is to be sensed as a pressure decrease or increase in flow rate at the crankcase vent tube pressure / flow rate sensor. In one example, manifold vacuum may be calculated and used to infer PCV valve position. If the crankcase is injured (cover removed, level bar out of position or crankcase vent tube disconnected from crankcase), then the high airflow rate while the PCV valve is open is not detectable. For example, the pressure drop does not occur or is noticeably reduced. The amplitude of the pressure drop or magnitude of the crankcase vent tube airflow rate also decreases as the area (opening area or opening size) of the injury increases. Oil cap loss and tubing separation will likely completely eliminate the debris. Some reduced drop may also occur with a level bar out of position.After determining a position and condition of a fault in the crankcase system at 406, 414, and 416, the routine proceeds to 418 to indicate the position and condition of the fault in the crankcase system by setting a diagnostic code. As such, a different diagnostic code may be set based on whether a fault is detected on the first side or the second side of the crankcase vent tube, and further based on the condition of the fault on the second side. At 420, a MIL may be illuminated and / or a message may be set to notify the operator of the condition and position of the crankcase system injury. At 422, one or more engine operating parameters may be adjusted to temporarily limit engine performance so as to reduce leakage of lubricant from the injured crankcase ventilation system and aspiration of lubricant into engine components (which may degrade engine operation).As such, if the crankcase ventilation tube is disconnected at the engine main air line (i.e., at the compressor inlet, also referred to herein as the first side), the high airflow rate while the PCV valve is fully open will be detectable. In one example, an engine control system may limit engine charging in response to the indication of a fault disposed on the first side of the crankcase vent tube or a fault disposed on the second side of the crankcase vent tube. For example, boosted engine operation may be discontinued.Turning now to FIG. 7, an example damage diagnostic of crankcase system integrity is shown in FIGS. 700, 710, and 720. More specifically, FIGS. 700-720 show transient crankcase vent tube (CVT) pressure drop characteristics during cranking at the respective upper plots (plots 702, 712, 722) and crankcase vent tube pressure drop characteristics as manifold air flow during engine running (steady state conditions) at the respective lower plots (plots 704, 714, 724). The upper plots of the maps are plotted versus time of engine operation, while the lower plots of the maps are plotted versus engine airflow rate (as depicted) along the x-axis.As discussed in greater detail above, the crankcase vent tube installation arrangement, as well as the specific position of the crankcase vent tube sensor within the tube, causes the crankcase vent tube to become under-pressurized at high engine airflow rates. Consequently, if the sensor detects the negative pressure, it can be determined that there is no injury and that the vent tube is properly attached. However, if the vacuum is not sensed, then a damage to crankcase system integrity is detected. As such, a separation of the vent tube at a side (a first side where it is connected to the air intake passage or a second side where it is connected to the crankcase) may result in reduced vacuum at high engine air flow rates (the degree of reduction in vacuum differing based on whether the injury is at the first or second side). Additionally, if separated on the second side, crankcase pulsations may not be sensed.FIG. 700 shows a first example where the amplitude of the transient drop in CVT pressure (plot 702) is greater than a threshold amount indicating sufficient airflow through the crankcase vent tube during engine cranking. Additionally, during engine operation, a decrease in steady state CVT pressure is proportional to an increase in steady state manifold air flow (plot 704). In other words, as engine air flow increases, a smaller but gradual flow passes through the vent tube and a corresponding vacuum is generated and sensed by a pressure or flow sensor in the crankcase vent tube.FIG. 710 shows a second example where the amplitude of the transient drop in CVT pressure (plot 712) is less than the threshold amount indicating insufficient airflow through the crankcase vent tube during engine cranking. Additionally, during engine operation, a decrease in steady state CVT pressure is not proportional to an increase in steady state manifold air flow, but the decrease is still greater than a threshold rate (plot 714). More specifically, during high engine air flow conditions (compared to the vacuum generated in the absence of injury, as shown at plot 704), a reduced vacuum is sensed by a pressure or flow sensor in the crankcase vent tube. Herein, responsive to the transient drop in crankcase vent tube pressure being less than the threshold amplitude and the decrease in crankcase vent tube pressure during the steady state manifold airflow increase being greater than the threshold rate, a damage to the crankcase ventilation system is indicated at the second side of the crankcase vent tube. The second side corresponds to a side where the crankcase ventilation tube is mechanically coupled to the crankcase. As detailed with FIG. 8, further, various damage to the crankcase system may be differentiated due to crankcase vent tube pressure and flow characteristics.FIG. 720 shows a third example, where the amplitude of the transient drop in CVT pressure (plot 722) is less than the threshold amount (in the depicted example, less than the amplitude of plot 702, but greater than the amplitude of plot 712), indicating insufficient air flow through the crankcase vent tube during engine cranking. Additionally, during engine operation, a decrease in steady state CVT pressure is not proportional to an increase in steady state manifold air flow (plot 724). More specifically, during high engine air flow conditions (compared to the vacuum generated in the absence of injury, as shown at plot 704), substantially no vacuum (zero vacuum) is sensed by a pressure or flow sensor in the crankcase vent tube. Herein, responsive to the transient drop in crankcase vent tube pressure being less than the threshold amplitude and the decrease in crankcase vent tube pressure during the steady state manifold airflow increase being less than the threshold rate, a damage to the crankcase ventilation system is indicated at the first side of the crankcase vent tube. The first side corresponds to a side where the crankcase ventilation tube is mechanically coupled to the air intake passage. For example, it may be indicated that the first side injury is due to the crankcase vent tube being separated from the air intake passage on the first side.Turning now to FIG. 8, an example damage diagnostic of crankcase system integrity is shown at FIGS. 800, 810, and 820 to distinguish between different conditions that may result in damage identified on the second side of the crankcase vent tube. More specifically, FIGS. 800-820 show transient crankcase vent tube pressure drop (CVT) during cranking characteristics at the respective upper plots (plots 802, 812, 822) and crankcase vent tube pressure drop characteristics with increasing manifold air flow during engine running (steady state conditions) at the respective lower plots (plots 804, 814, 824). All upper plots are plotted versus time of engine operation along the x-axis, while all lower plots are plotted versus engine air flow rates along the x-axis.FIG. 800 shows a first example of crankcase system injury on the second side of the crankcase vent tube caused by a crankcase oil fill port cap releasing. Herein, an amplitude of the transient drop in CVT pressure (plot 802) is less than the threshold amount, indicating insufficient air flow through the crankcase vent tube during engine cranking. Also, during engine running, a decrease in steady state CVT pressure is not proportional to an increase in steady state manifold air flow. Specifically, after a threshold level of engine air flow (plot 804), no vacuum is sensed by a pressure or flow sensor in the crankcase vent tube. Herein, further based on an opening amount of the injury being greater than a threshold amount, a condition of a missing oil cap is indicated.FIG. 810 shows a second example of crankcase system injury to the second side of the crankcase vent tube caused by a crankcase oil level rod being offset. Herein, an amplitude of the transient drop in CVT pressure (plot 812) is less than the threshold amount, indicating insufficient air flow through the crankcase vent tube during engine cranking. Additionally, during engine operation, a decrease in steady state CVT pressure is not proportional to an increase in steady state manifold air flow (plot 814). Specifically, during high engine air flow conditions, no vacuum is sensed by a pressure or flow sensor in the crankcase vent tube. Herein, further based on an opening amount of the injury being less than a threshold amount, a state of a missing level spike is indicated.It will be appreciated that in embodiments where the crankcase ventilation tube includes a venturi with a coupled pressure sensor, responsive to an oil cap becoming dislodged or a level rod out of position, a large resultant air flow through the venturi may be sensed as a low vacuum by the coupled pressure sensor. As such, the vacuum created due to an oil cap becoming dislodged may be greater than the vacuum created due to the level bar being out of position.FIG. 820 shows a third example of crankcase system injury on the second side of the crankcase vent tube caused by the crankcase vent tube being blocked or clogged on the second side. Herein, an amplitude of the transient drop in CVT pressure (plot 822) is less than the threshold amount, indicating insufficient air flow through the crankcase vent tube during engine cranking. Also, during engine running, an increase in steady state CVT pressure is observed during an increase in steady state manifold air flow. More specifically, during high engine air flow conditions, a high (positive) pressure is sensed by a pressure or flow sensor in the crankcase vent tube. In response to these conditions, a blockage of the crankcase vent tube is detected on the second side (coupled to the crankcase.In this way, an existing sensor used to monitor the crankcase ventilation system may be used to also reliably identify a position and condition of damage to the crankcase system integrity.Turning now to FIG. 5, an example method 500 is shown for indicating degradation of a PCV valve (i.e., a valve coupled into a positive crankcase ventilation line between a crankcase and an intake manifold) based on changes in crankcase ventilation tube pressure and / or airflow rate during engine cranking. As such, the routine of FIG. 5 may be executed after confirming whether a crankcase injury has been detected based on transient waste characteristics.As such, the method of FIG. 5 evaluates the PCV flow characteristics during engine running (or during a maintenance operation), provided that both the pressure decrease across the PCV valve (ManVac) and the flow rate through the valve (CVT flow rate) are measured by the CVT pressure sensor. In some embodiments of FIG. 5, the method may simply verify the CVT flow rates at given ManVacs. Therein, at the most restricted PCV valve position, the CVT flow rate will be substantially low so that it is in noise. At the position with the least throttled flow rate, the flow rate will be significant (i.e., a transient drop will be seen).At 502, the routine includes confirming that the engine intake air flow rate is less than a threshold flow rate. In one example, the engine intake air flow rate may be lower than the threshold flow rate during engine cranking and early ramp-up when engine speed is slower than a threshold speed and before a threshold number of combustion events has occurred. Next, at 504, it may be confirmed that the manifold vacuum is lower than a threshold vacuum level. For example, it may be confirmed that the manifold negative pressure is lower than 40 kPa. If the manifold vacuum is not less than the threshold, then at 505, an actuator may be adjusted to ensure a desired manifold vacuum level. For example, a throttle opening may be adjusted so as to maintain the manifold vacuum below the threshold vacuum level. As such, because the throttle opening is associated with a flow rate through a PCV valve, the throttle opening may be adjusted to ensure a manifold vacuum level (e.g., 13 kPa) such that maximum flow through the PCV valve is ensured.The routine of FIG. 5 uses the output of a crankcase vent tube pressure sensor to estimate degradation of the PCV valve. Specifically, a relative sensor in the crankcase vent tube may be advantageously used as a flowmeter to sense changes in the airflow rate in the crankcase vent tube. However, such a pressure sensor may correlate any vacuum in the crankcase vent tube as a flow rate. In other words, flow through the crankcase vent tube may be sensed as a vacuum at the crankcase vent tube pressure sensor, and similarly a vacuum in the crankcase vent tube may be sensed as a vacuum at the crankcase vent tube pressure sensor. Thus, by performing the diagnostic routine, when the engine intake air flow rate is less than a threshold flow rate, only during conditions when the engine intake air flow rate itself does not cause a vacuum to be sensed is set to an output of a crankcase vent tube pressure sensor. Likewise, by performing the diagnostic routine, when a manifold vacuum is lower than a threshold vacuum level, only during conditions when the manifold vacuum itself does not cause a vacuum to be sensed, a crankcase vent tube pressure sensor output is set. Additionally, during conditions when engine intake air flow is low and manifold vacuum is low (i.e., during engine cranking and early ramp-up), an air flow rate through the crankcase vent tube is expected to be high. Thus, by conducting the diagnostics during these conditions, PCV valve diagnostics based on changes in crankcase vent tube airflow are enabled only when there is sufficient airflow through the vent tube for a reliable diagnostic.At 506, the routine includes determining an expected crankcase vent tube pressure and / or air flow profile based on the current engine intake air flow and manifold vacuum levels. The expected profiles may include an expected vent tube pressure and an expected vent tube flow rate for a given engine speed. At 508, the routine includes estimating an actual crankcase vent tube pressure and / or airflow profile based on the output of the crankcase vent tube pressure sensor. It will be appreciated that in alternative embodiments, the estimated profile may be based on the output of a dedicated crankcase vent tube flow sensor or a pressure sensor coupled to the neck of a crankcase vent tube venturi. The estimated profiles may include a measured and / or inferred vent tube pressure and a measured and / or inferred vent tube flow rate for the given engine speed.As such, during engine cranking and subsequent ramp-up, the PCV valve is first in a more open position (e.g., a maximum open position when manifold vacuum is lower and throttle opening is small). During these conditions, the airflow through the crankcase vent tube is substantially higher and may be estimated by the crankcase vent tube pressure / flow sensor as a transient increase in vent tube airflow or a transient increase in vent tube pressure. Thereafter, when engine speed is above a threshold and manifold vacuum is higher, the PCV valve may be in a second, less open, position (e.g., a position with a smaller fixed orifice that allows for lower flow). For example, in the second position, flow through the PCV valve to a sonic choked hole may be controlled. During these conditions, the air flow through the crankcase vent tube decreases and stabilizes to a steady state that can also be estimated by the crankcase vent tube pressure / flow sensor. If a PCV valve remains open, crankcase vent tube air flow may continue to increase at higher manifold vacuum conditions rather than decreasing and stabilizing at steady state value. Likewise, if the PCV valve becomes stuck in the small orifice position during cranking, crankcase vent tube airflow may not increase to expected values during lower engine vacuum conditions. Thus, by comparing the characteristic changes in an expected flow / pressure profile of a crankcase vent tube pressure with the actual changes in a crankcase vent tube flow / pressure profile as estimated by a crankcase vent tube pressure / flow sensor, degradation of the PCV valve may be identified.Accordingly, at 510, the measured or estimated crankcase vent tube pressure profile and / or air flow profile may be compared to the expected crankcase vent tube pressure profile and / or air flow profile and it may be determined if an absolute difference between the profiles is greater than a threshold. That is, it may be determined whether the expected and actual crankcase vent tube pressure values or flow rates differ by more than a threshold amount. If not, then at 512, the routine determines that there is no degradation to the PCV valve.If there is a deviation, then at 514, it is determined that the PCV valve may be degraded and the routine may proceed to determine the nature of the degradation based on the estimated crankcase vent tube pressure and / or flow rate profiles. Specifically, at 516, it may be determined whether the estimated crankcase vent tube pressure or air flow rate is greater than the expected crankcase vent tube pressure (or air flow rate) by more than the threshold amount. Alternatively, it may be determined whether an estimated amplitude of a transient drop in crankcase vent tube pressure is higher than an expected amplitude (or threshold amplitude). If so, then at 518, it may be determined that due to the PCV valve stuck in the open position, the estimated crankcase vent tube pressure / airflow profile is greater than the expected profile (or the amplitude of the transient drop in crankcase vent tube pressure is greater than an expected amplitude). The controller may display the same by setting a corresponding diagnostic code.If the estimated crankcase vent tube pressure or air flow rate is not greater than the expected crankcase vent tube pressure (or air flow rate), then it may be confirmed that the estimated crankcase vent tube pressure or air flow rate is less than the expected crankcase vent tube pressure (or air flow rate) by more than the threshold amount. Alternatively, it may be determined whether an estimated amplitude of a transient drop in crankcase vent tube pressure is less than an expected amplitude (or threshold amplitude). After confirmation, it may be determined at 522 whether a condition of crankcase injury has already been detected. As detailed above with reference to FIGS. 2A-B, a damage to crankcase ventilation system integrity may have been detected prior to initiating the PCV valve diagnostic routine of FIG. 5. As explained with reference to FIGS. 3-4, a damage to crankcase ventilation system integrity and a position of the damage may be determined based on characteristics of a transient drop in crankcase ventilation tube pressure during engine cranking and a steady state change in crankcase ventilation tube pressure relative to a steady state change in manifold air flow during engine running.As such, if there is a damage to crankcase system integrity, there may be a change in one or more of crankcase vent tube pressure and flow rate, both of which may have an effect on the output of the crankcase vent tube pressure / flow sensor and the resulting profile during engine cranking and start-up. In addition, the profile is influenced by the position of the crankcase injury. For example, damage to the crankcase system that occurs on the second side of the crankcase vent tube (i.e., the side of the crankcase vent tube coupled to the crankcase) may cause the crankcase vent tube flow rate to be substantially decreased due to the damage causing a short circuit at the expected flow rate. Additionally, the crankcase vent tube pressure sensor may no longer exhibit vacuum at high engine air flow rates (compared to the vacuum shown in the absence of injury at high engine air flow rates). Injuries on the second side of the vent tube that may cause these effects include, for example, separation of the vent tube from the crankcase on the second side, detachment of a crankcase oil fill port cap, or offset of a crankcase oil level rod. As another example, crankcase system injury occurring on the first side of the crankcase vent tube (i.e., the side of the crankcase vent tube coupled to the air intake passage) may cause the crankcase vent tube flow rate to remain substantially unaffected, but the crankcase vent tube pressure sensor may not exhibit vacuum at high engine air flow rates (compared to the vacuum shown in the absence of injury at high engine air flow rates). Injuries on the first side of the vent tube that may cause these effects include, for example, separating the vent tube from the air intake duct on the first side.Accordingly, if no crankcase injury has previously been detected, at 524, the routine determines that the estimated crankcase vent tube pressure / airflow profile is less than the expected profile (or that the amplitude of the transient drop in crankcase vent tube pressure is less than an expected amplitude) due to the PCV valve stuck in a low flow open position (e.g., a small orifice position or a closed position). The controller may display the same by setting a corresponding diagnostic code. As such, the diagnostic code set to indicate PCV valve degradation due to the valve stuck open (at 518) may be different from the diagnostic code set to indicate PCV valve degradation due to the valve stuck closed (at 524). If a crankcase violation was previously detected, at 526, the controller may determine that the PCV valve may be functional and not degraded.It will be appreciated that in some embodiments, in addition to confirming at 522 whether a crankcase system violation has been detected, it may also be determined whether an air intake filter has been diagnosed, and if so, a degree of air filter blockage may be included in the PCV valve diagnostic. As detailed with FIG. 10, if air filter plugging is confirmed, then at 524, the deviation between the expected profile and the estimated profile may be due to the air filter being clogged, rather than the PCV valve being stuck in the low flow position. The controller may distinguish between these conditions based on the (known) degree of filter plugging relative to the observed deviation between the estimated and expected crankcase vent tube flow rate profiles. For example, if the deviation is greater than the expected consideration in the degree of filter plugging, then a damage to the crankcase system may be determined.In this way, PCV valve degradation may be determined based on changes in airflow rate through a crankcase vent tube, as estimated by a crankcase vent tube pressure or flow sensor, during engine cranking. Based on deviations of an expected flow profile from an estimated flow profile, PCV valve degradation due to a stuck open valve may be better distinguished from degradation due to a stuck closed valve. By performing the PCV valve diagnostic routine after completing a crankcase system diagnostic routine, changes in crankcase vent tube pressure or flow caused due to a damage to the crankcase system on either a crankcase side or an air intake passage side of the crankcase vent tube may be included to enable reliable PCV valve diagnostic. Specifically, changes in crankcase vent tube airflow due to crankcase system injury (e.g., due to a separate vent tube or offset oil fill port cover) may be better distinguished from those due to a degraded PCV valve.In another example, in response to the PCV valve stuck open (or high flow position), engine boost may be limited so that MAP is below BP. As such, a stuck open PCV valve results in blow crankcase gases and oil mist into the inlet of the compressor. This leads to a risk of rapid oil consumption, which can be reduced by limiting (or interrupting) the charging. In comparison, a stuck closed PCV valve results in essentially a spaced crankcase ventilation system. Over a long term, this leads to engine mud formation in the oiled portions of the engine. Consequently, no remedial action may be necessary. Alternatively, in response to the PCV valve stuck closed (or n of the low flow position), an engine speed may be decreased.It will be appreciated that while the routine of FIG. 5 is depicted as being executed while an engine is cranking, in alternative embodiments, such as embodiments where the engine is coupled to a hybrid vehicle system, or in engine start-stop systems where the engine is configured to be selectively deactivated responsive to idle-stop conditions, the routine of FIG. 5 may also be executed during key-off conditions (i.e., where a vehicle operator has rotated an ignition key to an off position). For example, during a key-off condition, a controller may close an intake throttle and perform a vacuum decay check with the PCV valve at any given position. Thereafter, PCV valve degradation may be determined based on a rate of vacuum decay from the crankcase vent tube.An example PCV valve diagnostic is illustrated at FIG. 1000 of FIG. 10. More specifically, FIG. 1000 shows changes in crankcase vent tube airflow rate along the y-axis and changes in manifold vacuum along the x-axis. Plots 1002- 1008 depict example changes in vent tube flow rate versus manifold vacuum used to diagnose a PCV valve.Plot 1002 depicts a first plot of an expected change in crankcase vent tube airflow rate during engine cranking and cranking. As discussed in greater detail above, during engine cranking, when manifold vacuum is low (and throttle opening is small), the PCV valve may be in an open position causing a large amount of air to be directed from an intake air filter, through the crankcase vent tube, via the crankcase, into the intake manifold. As a result, at low manifold vacuum levels (e.g., at or around 13 kPa), a significantly high rate of air flow through the crankcase vent tube is seen. Thereafter, as the engine proceeds from cranking to cranking, a throttle opening may increase, a PCV valve opening may decrease (e.g., to a fixed smaller opening position or a low flow position), a manifold vacuum may increase (e.g., above 13 kPa), and the air flow into and through the crankcase vent tube may decrease, causing a decrease and ultimately stabilizing the crankcase vent tube air flow rate.The plot 1004 shows a second plot of an estimated change in crankcase vent tube airflow rate during engine cranking and start-up in the presence of a stuck open PCV valve. Herein, as the engine proceeds from cranking to cranking, the PCV valve opening does not decrease, as expected, due to the PCV valve stuck open. As a result, as manifold vacuum increases, the air flow into and through the crankcase vent tube may continue to increase, causing the estimated crankcase vent tube air flow rate and profile (plot 1004) to be higher than the expected air flow rate and profile (plot 1002).Plot 1006 shows a third plot of an estimated change in crankcase vent tube airflow rate during engine cranking and cranking in the presence of a stuck open PCV valve. Herein, during engine cranking, the PCV valve may not be able to open to the fully open position, causing a substantially smaller amount of air to be directed from the intake air filter, through the crankcase vent tube, via the crankcase, into the intake manifold. As a result, at low manifold vacuum levels, a significantly lower velocity of airflow through the crankcase vent tube is seen, causing the estimated crankcase vent tube airflow velocity and profile (plot 1006) to be lower than the expected airflow velocity and profile (plot 1002).Plot 1008 shows a fourth plot of an estimated change in crankcase vent tube air flow rate during engine cranking and cranking in the presence of a functional PCV valve and air filter that is fully clogged. Herein, as at plot 1006, during engine cranking, even though the PCV valve is open, air flow from the intake air filter, through the crankcase vent tube, via the crankcase, into the intake manifold may be decreased due to the clogged air filter. As a result, at low manifold vacuum levels, a significantly lower velocity of airflow through the crankcase vent tube is seen, causing the estimated crankcase vent tube airflow velocity and profile (plot 1006) to be lower than the expected airflow velocity and profile (plot 1002).In one example, plot 1002 is observed if the PCV valve is not degraded, plot 1004 is observed if the PCV valve is stuck in a low throttle position, plot 1006 is observed if the PCV valve is stuck in a high throttle position, and plot 1008 is observed if the air filter is stuck or stuck closedIt will be appreciated that while the example of FIG. 10 illustrates determining PCV valve degradation based on deviations in an estimated vent tube air flow rate profile from an expected air flow rate profile, in an alternative example, it may be determined (or illustrated) by deviations in an estimated vent tube vacuum profile from an expected vacuum profile. In this way, an existing sensor used to monitor the crankcase ventilation system may be advantageously used to reliably diagnose a PCV valve.Turning now to FIG. 6, an example method 600 is shown for indicating degradation of an intake air filter based on a crankcase vent tube pressure estimated by a pressure sensor in the crankcase vent tube. As such, the routine of FIG. 6 may be executed as part of the routine of FIGS. 2A-B.At 602, the routine includes confirming if the manifold air flow rate is less than a first threshold. By confirming that the manifold air flow rate is lower than the first threshold, it may be confirmed that sensor compensation is calculated during low engine flow conditions (such as while there is no engine flow rate) so as to reduce noise resulting from the calculation from the engine flow rate. Next, at 604, a crankcase vent tube pressure during low manifold air flow conditions may be estimated by a pressure sensor disposed in the crankcase vent tube. The pressure sensor in the crankcase vent tube may be, for example, an absolute pressure sensor or a relative pressure sensor. In embodiments where the pressure sensor is an absolute pressure sensor, it may or may not be coupled to an air pressure sensor. In embodiments where the pressure sensor is a relative sensor, an absolute air pressure sensor (e.g., BP sensor 57 of FIG. 1 ) may be coupled thereto (e.g., additionally present outside of the filtered volume) or used in conjunction.At 606, the routine includes calculating a sensor offset. Specifically, the algorithm used nulls the relative pressure sensor during low engine flow rates or experiences a sensor offset based on the barometric pressure indication from the BP sensor during low engine flow conditions. In this way, the controller learns or concludes the air pressure from the crankcase vent tube pressure sensor and may either use the output of the crankcase vent tube pressure sensor as air pressure itself at a low engine flow rate or may use the output to ensure a common and calibrated reference to air pressure measured separately. In one example, air pressure may be separately learned from a dedicated air pressure sensor coupled to the intake passage (e.g., upstream of the air filter), or from a compressor inlet pressure (CIP) sensor disposed in the inlet upstream of the compressor and downstream of the air filter. However, by using the existing crankcase vent tube pressure sensor to estimate the BP, the need for a BP sensor or a CIP sensor is reduced.In one example, the pressure sensor in the crankcase ventilation tube is a first pressure sensor, and the offset is determined based on a second pressure sensor (e.g., a BP sensor) coupled downstream of the air filter and upstream of the compressor. Specifically, the offset may be based on the output of the first pressure sensor relative to the output of the second pressure sensor during low manifold air flow conditions. For example, if the first pressure sensor is an absolute pressure sensor without a BP sensor, the output of the first pressure sensor may be used to conclude the BP. As another example, if the first pressure sensor is an absolute pressure sensor with a BP sensor, the difference between the outputs of the first pressure sensor and the coupled BP sensor may be used to infer the BP and learn a sensor offset. As yet another example, if the first pressure sensor is a relative pressure sensor, the difference of the first pressure sensor from a null indicator may be used to conclude the BP and calculate a sensor offset.The calculated offset may then be stored in the controller's memory as a reference pressure. The stored offset may then be retrieved and applied during subsequent higher engine flow conditions to determine air filter plugging, as detailed below.Next, at 608, it may be determined if the engine airflow (or other signal associated with the engine airflow rate) is greater than a second threshold. By confirming that the engine air flow rate is higher than the second threshold, it may be determined that air filter plugging is estimated when the effect of air filter plugging on crankcase vent tube pressure is greater during higher engine flow conditions so as to improve sensing accuracy. If the engine air flow rate is not higher than the second threshold, the routine may wait until desired engine air flow levels are reached to perform the air filter plugging diagnostic. At 610, upon confirming that the manifold air flow levels are higher than the second threshold, it may be confirmed that the sensor offset has been updated. This may include confirming that the sensor offset experienced during conditions of lower engine flow immediately preceding conditions of higher engine flow has been stored in the controller (e.g., a lookup table has been updated with the most recently experienced sensor offset).At 612, upon confirming that the offset has been updated, the sensor output(s) may be adjusted based on the updated offset. This includes adjusting the output of the crankcase vent tube pressure sensor with the updated offset. At 614, it may be determined whether the deviation between the adjusted sensor output and an estimated / inferred BP is greater than a threshold. In one example, the deviation may be based on the difference between the sensors. In another example, the deviation is based on a relationship between the sensor outputs. If the difference is not greater than the threshold measure, then at 616, it may be determined that the air filter is clean and not clogged. In comparison, if the difference is greater than the threshold measure, then at 618, an air filter plugging may be indicated. A degree of air filter plugging may be determined based on the difference between the adjusted sensor output and the BP (e.g., relative to the threshold).In an alternative example, a deviation may be calculated between the indication of crankcase vent tube pressure at a high airflow (which is substantially equal to CIP) and the reference pressure estimated at a low airflow. Thereafter, a reference air filter differential pressure may be retrieved from a look-up table. The controller may then balance the reference air filter differential pressure for actual conditions and calculate a plugging factor from the ratio of delta CIP to the compensated reference differential pressure. That is, the controller may estimate an instantaneous air filter plugging factor based on a ratio of the difference between crankcase vent tube pressures estimated during high and low air flow conditions relative to a reference air filter decrease, with an improper temperature and pressure (STP) correction factor. In one example, the STP conditions include 103 kPa and 100°F. As an example, the controller may estimate the congestion factor using the following equation: wherein the congestion factor is determined with reference to standard conditions (STP).At 620, the controller may set a diagnostic code to indicate air filter plugging. As such, the diagnostic code to indicate air filter plugging may be different than a diagnostic code used to indicate damage / degradation to the crankcase ventilation system. The controller may also illuminate a MIL light that indicates to the vehicle operator to service the air filter. The controller may also limit engine power so as to reduce compressor over-rotation and over-heating that may be caused due to the clogged air filter.In this way, by indicating air filter degradation based on crankcase vent tube pressure, monitoring both crankcase system integrity and air filter plugging may be performed using a single sensor set already present in the crankcase vent tube.An example air filter plugging diagnostic is illustrated in FIG. 900 of FIG. 9. More specifically, FIG. 900 shows changes in crankcase vent tube pressure along the y-axis and changes in manifold air flow along the x-axis. Plots 902-906 depict example changes in vent tube pressure versus manifold air flow used to indicate a condition of an intake air filter.During low engine air flow conditions, such as before the manifold air flow is at a first threshold AF 1, an offset may be experienced for the crankcase vent tube pressure sensor. For example, if the crankcase vent tube pressure sensor is an absolute pressure sensor, air pressure may be inferred based on the output of the crankcase vent pressure sensor or due to an offset between the vent tube pressure sensor and a coupled BP sensor. Referring to FIG. 900, P 1 (which extends as a dashed line across the map) reflects the inferred reference BP when the crankcase vent tube pressure sensor is in absolute pressure sensor. In an alternative example, the crankcase vent tube pressure sensor may be a relative pressure sensor, wherein an offset of the pressure sensor indicator from a null indicator is learned such that P 1 on FIG. 900 reflects a compensated reference null pressure.During conditions of average manifold air flow, i.e., when the manifold air flow is higher than the first threshold AF 1 but lower than a second threshold AF 2, no offset may be experienced or applied. Thereafter, when conditions of high manifold air flow are reached, such as when the manifold air flow is higher than the second threshold AF 2, the learned offset may be applied to determine an air filter plugging factor.Plot 902 shows deviations in crankcase vent tube pressure from reference P 1, as estimated by a crankcase vent tube pressure sensor, relative to changes in manifold air flow in the absence of air filter plugging (i.e., a clean air filter). Plot 904 shows a corresponding deviation in crankcase vent tube pressure from P 1 relative to manifold air flow when the air filter is partially clogged. Plot 906 shows changes in crankcase vent tube pressure versus manifold air flow when the air filter is dirty and substantially clogged. As can be seen by comparing the plots 902 to 906, as the clogging factor of the air filter increases, a deviation of the pressure from the reference P 1 increases. A controller may determine the degree of filter plugging based on the degree of deviation. In this way, an existing sensor used to monitor the crankcase ventilation system may be advantageously used to also reliably diagnose air filter plugging.In this way, by disposing a pressure sensor within a crankcase vent tube, changes in pressure and air flow through the vent tube may be monitored while the sensor is housed in a cost effective manner. By correlating the estimated changes in crankcase vent tube pressure with expected values, crankcase system integrity, air filter degradation, and PCV valve degradation may be reliably indicated. By provoking properties of crankcase vent tube pressure and flow data during engine cranking and running, injuries in the crankcase ventilation system located on a side of the vent tube coupled to an air intake passage may be better distinguished from those occurring on a side of the vent tube coupled to a crankcase. By making adjustments to a throttle and / or PCV valve to increase intake manifold vacuum during engine cranking, a precision of detecting crankcase damage may be increased. By using the crankcase ventilation system pressure sensor also to identify air filter plugging as well as PCV valve degradation, the need for additional sensors and valves to monitor air filter degradation and PCV valve degradation may be reduced, which provides cost and complexity reduction advantages without reducing the accuracy of degradation detection. Further, an engine crankcase ventilation system may remain active during diagnostic operations.It will be appreciated that the configurations and methods disclosed herein are exemplary in nature and that these specific embodiments are not to be considered in a limiting sense because numerous variations are possible. For example, the above technology can be applied to V6, R4, R6, V12, Boxer-4, and other types of motors. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and / or characteristics disclosed herein.The following claims particularly emphasize certain combinations and sub-combinations that are considered novel and not obvious. These claims may refer to "a" element or "a first" element or the equivalent thereof. Such claims should be understood to include inclusion of one or more such elements, with neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and / or characteristics may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal or different in scope to the original claims, are also considered to be within the scope of the present disclosure.

Claims

A method for an engine crankcase ventilation system, comprising: at engine (10), reducing an opening of a PCV valve (78) to a low flow position, the PCV valve (78) coupled in a PCV conduit (76) between an intake manifold (15) and a crankcase (28), the intake manifold (15) being located downstream of a throttle (44), distinguishing a disconnection of a crankcase ventilation tube (74) from degradation of the PCV valve (78) based on characteristics of a transient drop of a crankcase ventilation tube pressure, setting a diagnostic code based on whether the crankcase ventilation tube (74) is disconnected or whether the PCV valve (78) is degraded, wherein a first side (101) of the crankcase vent tube (74) is coupled to a fresh air intake passage (13) upstream of a compressor (50) and a second side (102) of the crankcase vent tube (74) is coupled to the crankcase (28).The method of claim 1, wherein the method further comprises indicating degradation of the PCV valve (78) based on characteristics of the transient drop in crankcase vent tube pressure, and wherein the crankcase vent tube pressure is estimated by a pressure sensor positioned in the crankcase vent tube (74).The method of claim 2, wherein based on transient droop characteristics, comprising based on a transient droop amplitude.The method of claim 3, wherein starting the engine (10) while the engine (10) is starting from start and before fuel is injected into an engine cylinder.The method of claim 4, wherein starting the engine (10) before an engine speed is an idle speed and while an intake manifold air flow is below a threshold.The method of claim 5, further comprising, upon cranking the engine (10), increasing the opening of an intake throttle to increase intake manifold vacuum to a threshold.The method of claim 6, wherein the displaying is performed after performing a crankcase injury detection routine.The method of claim 1, wherein the crankcase ventilation tube pressure is derived from a flow sensor positioned in the crankcase ventilation tube (74), the flow sensor including a venturi tube.A method for an engine (10), comprising: upon cranking the engine (10): reducing an opening of a PCV valve (78) to a low flow position, the PCV valve (78) coupled in a PCV conduit (76) between an intake manifold (15) and a crankcase (28), the intake manifold (15) being disposed downstream of a throttle (44); distinguishing a disconnection of a crankcase vent tube (74) from degradation of the PCV valve (78) based on characteristics of a transient drop of a crankcase vent tube pressure; setting a diagnostic code based on whether the crankcase vent tube (74) is disconnected or whether the PCV valve (78) is degraded, wherein a first side (101) of the crankcase vent tube (74) is coupled to a fresh air intake passage (13) upstream of a compressor (50) and a second side (102) of the crankcase vent tube (74) is coupled to the crankcase (28).The method of claim 9, the method further comprising: indicating degradation of the PCV valve (78) based on deviations of an estimated crankcase vent tube pressure profile from an expected crankcase vent tube pressure profile, the expected profile based on engine speed and manifold vacuum settings, wherein the indicating is performed under engine cranking conditions when the manifold vacuum is less than a threshold.The method of claim 10, wherein the engine (10) is coupled to a vehicle and wherein the displaying is performed under key-off conditions.The method of claim 10, wherein the indicating comprises: if the estimated crankcase vent tube pressure profile is greater than the expected crankcase vent tube pressure profile, indicating that the PCV valve (78) is stuck in a high flow position; and if the estimated crankcase vent tube pressure profile is less than the expected crankcase vent tube pressure profile, indicating that the PCV valve (78) is stuck in a low flow position.The method of claim 12, further comprising setting a first diagnostic code to indicate that the PCV valve (78) is stuck in the high flow position and setting a second, different diagnostic code to indicate that the PCV valve (78) is stuck in the low flow position.The method of claim 13, further comprising limiting an engine speed in response to the indication of valve degradation.The method of claim 10, wherein the estimated crankcase vent tube pressure profile is estimated by a pressure or flow sensor coupled to the crankcase vent tube (74), the crankcase vent tube (74) positioned outside the engine (10).An engine crankcase ventilation system comprising: an engine (10) including a fresh air intake passage (13) and a crankcase (28); a crankcase ventilation tube (74) mechanically connected to the fresh air intake passage (13) upstream of a compressor (50), the crankcase ventilation tube (74) also mechanically connected to the crankcase (28) via an oil separator (81), the crankcase ventilation tube (74) being located outside the engine (10); a PCV valve (78) coupled between the crankcase (28) and an intake manifold (42) in a PCV conduit (76), the intake manifold (42) being located downstream of a throttle (44); a flow sensor coupled within the crankcase vent tube (74) for estimating airflow through the crankcase vent tube (74); and a control system having computer readable instructions for: upon cranking the engine (10), decreasing an opening of the PCV valve (78) to a low flow position, distinguishing a disconnection of the crankcase vent tube (74) from degradation of the PCV valve (78) based on characteristics of a transient drop of a crankcase vent tube pressure, setting a diagnostic code based on whether the crankcase vent tube (74) is disconnected or whether the PCV valve (78) is degraded,The system of claim 16, wherein the control system includes further instructions for estimating a change in airflow through the crankcase vent tube (74), indicating degradation of the PCV valve (78) based on the estimated change in airflow through the crankcase vent tube (74) deviating more than a threshold from an expected change in airflow, and indicating a condition of the PCV valve degradation based on the estimated change in the expected change, the indicating comprising: indicating that the PCV valve (78) is stuck in a high flow position based on the estimated change being greater than the expected change, and indicating, the PCV valve (78) stuck in a low flow position based on the estimated change being less than the expected change.The system of claim 17, wherein the control system further includes instructions to limit engine charging in response to the indication that the crankcase ventilation tube (74) is disconnected.

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