Method for testing a pressure sensor of an internal combustion engine, in particular of a motor vehicle

Abstract

The invention relates to a method for testing a first sensor (13) designed to detect the pressure of a fuel intended for operating an internal combustion engine (1), in which method a measured variable characterising an air-fuel ratio of the internal combustion engine (19) is measured by means of a second sensor (14) provided in addition to the first sensor (13). An electronic computing device (15) is used to determine a first actual value which characterises the measured variable measured by means of the second sensor (14) and thereby the air-fuel ratio of the internal combustion engine (1). The first actual value is compared with a first setpoint value. In order to test the first sensor (13), a diagnosis is performed which is carried out depending on a result of the comparison of the first actual value with the first setpoint value.

Description

[0001] Method for testing a pressure sensor of an internal combustion engine, in particular of a motor vehicle

[0002] The invention relates to a method for testing a pressure sensor of an internal combustion engine, in particular of a motor vehicle, according to the preamble of patent claim 1.

[0003] US Pat. No. 8,706,383 B2 discloses a control system. DE 10 2010 044 164 A1 discloses a method for diagnosing a malfunction of a sensor system in an air system of an internal combustion engine. Furthermore, EP 4 062 141 A1 and WO 2021 / 098937 A1 disclose a method for detecting an operating deviation of a pressure sensor for a piston internal combustion engine.

[0004] The object of the present invention is to provide a method for testing a pressure sensor of an internal combustion engine, so that the pressure sensor can be tested particularly advantageously.

[0005] This object is achieved according to the invention by a method having the features of patent claim 1. Advantageous embodiments of the invention are the subject of the dependent claims.

[0006] The invention relates to a method for testing a first sensor designed to detect the pressure of a fuel provided for operating an internal combustion engine. The fuel is preferably a liquid fuel. The internal combustion engine, also referred to as an internal combustion engine, motor, or internal combustion engine and preferably designed as a reciprocating piston engine, i.e., as a reciprocating piston motor, can be operated in a fired mode using the fuel. During fired mode, combustion processes take place in the internal combustion engine, in particular in at least one combustion chamber of the internal combustion engine. During each combustion process, a respective fuel-air mixture, which is also simply referred to as a mixture, is combusted, in particular ignited and combusted. The respective fuel-air mixture comprises air and the aforementioned, preferably liquid, fuel.The first sensor is intended or designed to detect, i.e., measure, the fuel pressure, also referred to as fuel pressure. Therefore, the first sensor is a pressure sensor, or the first sensor is also referred to as a pressure sensor.

[0007] In the method, which is carried out by means of an electronic computing device, also referred to as a control unit or embodied as a control unit, a measured variable is measured, i.e., recorded, by means of a second sensor provided in addition to the first sensor. In particular, the second sensor is arranged outside the first sensor, which is preferably arranged outside the second sensor. The measured variable characterizes a combustion air ratio of the internal combustion engine, also referred to as lambda (A).As is well known from the general state of the art, the combustion air ratio characterizes the fuel-air mixture, and thus a composition of the fuel-air mixture, in particular in such a way that the combustion air ratio sets the air mass actually available for the combustion of the mixture or for the combustion of the fuel in the mixture in relation to the minimum air mass theoretically required for stoichiometric combustion of the mixture or of the fuel in the mixture. For example, the second sensor is a lambda probe, which measures the measured variable, for example, at a point in an exhaust passage of the internal combustion engine through which exhaust gas from the internal combustion engine flows. The exhaust gas results from the combustion of the mixture.Thus, for example, the measured variable is or characterizes a residual oxygen content in the exhaust gas of the internal combustion engine.

[0008] By means of the electronic computing device, at least a first actual value is determined, which characterizes the measured variable measured by the second sensor and thus the combustion air ratio of the internal combustion engine characterized by the measured variable. For example, the second sensor provides a signal, in particular an electrical signal, which is received, for example, by the electronic computing device. The signal comprises, for example, the actual value, so that, for example, the electronic computing device determines the actual value by the electronic computing device receiving the signal. Furthermore, it is conceivable that, in particular by means of the electronic computing device, the actual value is determined from the signal, in particular generated and thereby determined.In the method, in particular by means of the electronic computing device, the first actual value is compared with a first target value, which is also referred to as the first comparison value or first reference value.

[0009] To test the first sensor, a diagnosis, also referred to as a sensor diagnosis, diagnostic function, or sensor diagnostic function, is carried out, in particular by means of the electronic computing device, depending on a result of the comparison of the first actual value with the first target value. For example, the diagnosis is carried out if and preferably only if it is determined based on the comparison of the first actual value with the first target value that the first actual value deviates from the first target value, in particular such that a deviation of the first actual value from the second target value exceeds a particularly predeterminable or predetermined threshold value.

[0010] In the method according to the invention, the diagnosis comprises the electronic computing device comparing at least a second actual value, which characterizes the fuel pressure measured by the first sensor, with a second target value, which is also referred to as a second reference value or second comparison value. The aforementioned measured variable is also referred to as the first measured variable. When reference is made previously and hereinafter to the measured variable, this refers to the first measured variable unless otherwise stated. It can be seen that the pressure is a second measured variable that can be detected, i.e. is to be measured, by the first sensor. In particular, the method, in particular the diagnosis, provides that pressure (second measured variable) is measured, i.e. detected, by the first sensor.For example, the electronic computing device determines the second actual value, which characterizes the fuel pressure measured by the first sensor. The aforementioned signal is also referred to as the first signal. When reference is made to the signal above and below, this refers to the first signal unless otherwise stated. The first sensor, for example, provides a second signal, in particular an electrical one, which characterizes the pressure measured by the first sensor. In this case, the electronic computing device, for example, receives the second signal. The second signal comprises, for example, the second actual value, so that, for example, the electronic computing device determines the second actual value by receiving the second signal.Furthermore, it is conceivable that the electronic computing device determines the second actual value from the second signal, in particular generates it and thereby determines it.

[0011] Furthermore, the diagnosis includes checking the first sensor depending on the comparison of the second actual value with the second target value.

[0012] For example, it is provided that the internal combustion engine is operated depending on the diagnosis, in particular depending on a result of the diagnosis. Preferably, the internal combustion engine is a component of a motor vehicle, also simply referred to as a vehicle, which is designed, for example, as a motor vehicle, in particular as a passenger car, and is drivable by means of the internal combustion engine. In particular, it is conceivable that the motor vehicle is driven by means of the internal combustion engine in the method. In particular, it is possible for the motor vehicle to be operated depending on the diagnosis, in particular depending on a result of the diagnosis.The diagnosis-dependent operation of the internal combustion engine and / or the motor vehicle comprises, for example, at least one function of the internal combustion engine and / or the motor vehicle being performed as a function of the diagnosis, in particular as a function of a result of the diagnosis. The function, i.e., the performance of the function, comprises, for example, at least one indication signal being output, in particular in an interior of the motor vehicle, also referred to as the passenger cell or passenger compartment, by means of an electrical or electronic reproduction device, wherein the indication signal is visually and / or haptically and / or acoustically perceptible to a person.

[0013] It can be seen that in the method according to the invention the diagnosis, i.e. its implementation, depends on the result of the comparison of the first actual value with the first target value. The diagnosis is also referred to as the first diagnosis. When reference is made to the diagnosis above and below, this means the first diagnosis unless otherwise stated. Since the sensor is checked during the diagnosis, the diagnosis is also referred to as sensor diagnosis. The comparison of the first actual value with the first target value takes place, for example, during a second diagnosis, which is also referred to as mixture diagnosis, since the first actual value characterizes the combustion air ratio and thus the mixture or its composition. Thus, the invention provides that the sensor diagnosis depends on the mixture diagnosis and is therefore carried out as a function of the mixture diagnosis.This allows the first sensor to be tested particularly advantageously. The first sensor is, for example, a component of a motor vehicle system by means of which the internal combustion engine is supplied with fuel. The invention makes it possible to specifically determine, in the event of a problem in the fuel system, whether this problem was caused by a fault in the first sensor or not. As a result, it is thus possible to exclude or confirm the first sensor as the source of the problem. Compared to conventional solutions, the invention improves the robustness of the diagnosis. The number of incorrect diagnoses caused in conventional solutions, for example by overshoots or reheating, can be significantly reduced compared to conventional solutions.Furthermore, the invention makes it possible to impair the fuel system only in the event of an actual fault, and thus as needed, and for example, only when the mixture diagnosis detects a fault or deviation in the mixture formation by which or during which the mixture is formed. A deviation or error in the mixture formation is determined, for example, when or in that the first actual value deviates from the first target value, or a deviation of the first actual value from the second target value is greater than the aforementioned threshold value. Furthermore, the invention enables particularly high robustness with regard to fault detection.

[0014] In order to be able to test the first sensor particularly precisely and robustly, one embodiment of the invention provides that the same value is always used as the second target value.

[0015] A further embodiment is characterized in that the second target value is a fixed value stored, in particular, in an electrical or electronic data memory of the electronic computing device, which is retrieved from the data memory. This enables a particularly precise and robust test of the first sensor.

[0016] In a further, particularly advantageous embodiment of the invention, it is provided that if it is determined based on the comparison of the second actual value with the second target value that the second actual value deviates from the second target value or that a deviation of the second actual value from the second target value exceeds a predeterminable or predetermined limit, a fault in the first sensor is detected. This allows the diagnosis to be carried out particularly precisely and robustly, in particular to the extent that, in the event of a problem with the fuel system, the first sensor can be excluded or confirmed as the source of the fault.

[0017] In order to be able to test the first sensor particularly advantageously, a further embodiment of the invention provides that the error is determined as a drift of the first sensor, also referred to as sensor drift. Thus, the diagnosis is also referred to, for example, as drift diagnosis.

[0018] In order to be able to carry out the diagnosis particularly precisely and robustly, it is provided in a further embodiment of the invention that, as a result of the determination of the error, data which characterize the error are stored in an error memory of the electronic computing device, the error memory of which is, for example, the aforementioned data memory or is a part of the data memory.

[0019] In a further, particularly advantageous initial situation of the invention, it is provided that at least one injection valve, by means of which the fuel can be introduced, in particular directly injected, into at least one combustion chamber of the internal combustion engine, is operated depending on a result of the diagnosis. Thus, for example, the aforementioned function can include the injection valve being operated depending on the diagnosis, i.e., depending on a result of the diagnosis.

[0020] Another embodiment is characterized by a pump for pumping the fuel. The fuel pump is also referred to as the first pump. When reference is made to the pump above and below, this refers to the first pump unless otherwise stated. For example, the pump can achieve the aforementioned fuel pressure by pumping the fuel, i.e., by pumping the fuel.

[0021] It has proven particularly advantageous if the fuel pump is operated based on the diagnostic result. This can, for example, compensate for a possible sensor error.

[0022] Finally, it has proven particularly advantageous to implement an advantageous test of the first target value if a second pump is provided in addition to the pump. The second pump is preferably arranged outside the first pump, which is preferably arranged outside the second pump. The aforementioned fuel pressure is also referred to as the first pressure. When pressure is mentioned above and below, this means the first pressure unless otherwise stated. The first fuel pressure can be or is brought about and effected by means of the first pump by conveying the fuel, and the fuel can be or is conveyed to the second pump by means of the first pump by conveying the fuel. As a result, the second pump can be or is supplied with the fuel conveyed by means of the first pump and having the first pressure.By means of the second pump, a second fuel pressure which is higher than the first pressure can be or is brought about or effected by means of the fuel being delivered, and by means of the second pump, the fuel can be or is delivered to at least one component of the internal combustion engine provided in addition to the pumps, so that the component can be or is supplied with the fuel having the second pressure and delivered by the second pump. For example, the component is or comprises the aforementioned injection valve. Furthermore, it is conceivable for the component to have a fuel distribution element, also referred to as a rail or common rail, in which, for example, the fuel having the second pressure can be or is received at least temporarily.The fuel distribution element can, for example, supply the injection valve, by means of which the fuel can be introduced, in particular injected, into the combustion chamber, in particular at the second pressure, in particular directly.

[0023] The aforementioned fuel system thus has, for example, a low-pressure region, which is also referred to as a low-pressure system. Furthermore, the fuel system has, for example, a high-pressure region, which is also referred to as a high-pressure system. The fuel has the first pressure in the low-pressure region, which is lower than the second pressure, so that the first pressure is referred to as low pressure. The fuel has the second pressure in the high-pressure region, which is higher than the first pressure, so that the second pressure is also referred to as high pressure.

[0024] Preferably, the first sensor is a low-pressure sensor, by means of which the first pressure (low pressure) is measured, i.e., recorded, as the pressure measured by the first sensor. The invention enables the first sensor, designed as a low-pressure sensor, to be tested particularly precisely and robustly. The invention is based in particular on the following findings and considerations: The low-pressure system is responsible, for example, for providing the fuel, also referred to as fuel supply. The low-pressure system can supply fuel to downstream components of an injection system.If, for example, the internal combustion engine has an intake manifold injection system, which, for example, has the aforementioned injection valve, by means of which the fuel can be injected at a point upstream of the combustion chamber into an intake tract through which air can flow, and in this case, for example, an intake manifold, then the intake manifold injection system or the injection valve can be supplied with the low-pressure fuel. Furthermore, it is conceivable to supply the second pump, also referred to as the high-pressure pump, which is a component of the high-pressure system, with the fuel having the first pressure delivered by the first pump, so that, for example, the high-pressure system is one of the downstream components.Thus, for example, the internal combustion engine has direct injection or a direct injection system, which, for example, requests low pressure from the first pump and is therefore supplied with the requested low pressure by means of the low-pressure system and thus by means of the first pump. By means of the first sensor, designed as a low-pressure sensor, it is measured, for example, whether the first pressure achieved and thus set by the first pump as the actual pressure corresponds to a desired setpoint pressure requested, for example, by the high-pressure system. In this case, the second actual value is or characterizes the actual pressure, wherein, for example, the second setpoint value characterizes, describes, or indicates the setpoint pressure.The correctly set actual pressure is crucial for the advantageous, desired functioning of components downstream of the low-pressure system, which are to be or are supplied with the fuel at the first pressure (low pressure) via the low-pressure system and thus via the first pump. Since, for example, the components downstream of the low-pressure system are used to introduce the fuel into the combustion chamber and thus form the mixture, thus carrying out the aforementioned mixture formation, the correctly set actual pressure is crucial or influencing the correct metering of a mass of fuel, the mass of which is introduced into the combustion chamber and thus injected. The low pressure therefore influences mixture formation.For example, in intake manifold injection, an injection time during which the fuel is injected, in particular by means of the injection valve, in particular directly into the intake manifold, in particular continuously, is set or determined as a function of the pressure measured by the first sensor. If, for example, the pressure measured by the first sensor is higher than the actual and therefore real fuel pressure prevailing in the fuel system, the injection time is too long, so that too much fuel is injected, which results in the mixture becoming or being rich, in particular undesirably. If the pressure measured by the first sensor is lower than the actual fuel pressure prevailing in the fuel system, the injection time is too short, so that too little fuel is injected, which results in the mixture being lean, in particular undesirably.If the mixture is undesirably rich or too rich, or if the mixture is undesirably lean or too lean, this can lead to undesirable effects such as undesirable emissions.

[0025] One fault pattern that can occur in the first sensor, for example a low-pressure sensor, is the previously mentioned drift, also known as sensor drift. In measurement technology, drift refers to a slow, unwanted change in a value or system property, for example due to aging or changes in ambient conditions. For example, if the first sensor measures a pressure of 5 bar, while the actual fuel pressure in the fuel system is only 2 bar, the first sensor has a drift of 3 bar. Conventionally, the diagnosis for testing the first sensor, which is particularly designed as drift diagnosis, is carried out completely independently of the mixture diagnosis. Furthermore, the diagnosis, which is particularly designed as drift diagnosis, is conventionally diagnosed when a pressure threshold is exceeded.In this regard, if, for example, the pressure measured by the first sensor exceeds a threshold that is set so high that this threshold cannot actually occur in the fuel system, especially in the low-pressure system, a fault is assumed, which is then reported. In other words, the threshold is set so high that it is physically unrealistic or even impossible for the low-pressure system. For example, 8 bar is selected as the threshold if the maximum expected pressure in the fuel system, especially in the low-pressure system, is 7 bar. Conventional, passive diagnostic functions have been identified as inadequate, especially for low-pressure systems, since with low low-pressure target values ​​it is possible that the threshold is not exceeded despite a fault being present.Furthermore, an excessive number of sensors is required to diagnose the first sensor. The aforementioned problems and disadvantages can now be avoided by the invention. In particular, the invention makes it possible to assign a deviation, in particular an excessive deviation (also referred to as a mixture deviation), of the first actual value from the first target value to a clear cause, which is in particular a drift of the first sensor, by carrying out the diagnosis as a function of the mixture diagnosis. The invention takes advantage of the fact that an error such as a drift of the first sensor leads to a mixture deviation, and thus to the first actual value deviating from the first target value, in particular an excessive deviation. If this is the case, the diagnosis is carried out to check whether the deviation of the first actual value from the first target value is due to an error such as a drift of the first sensor.

[0026] Further advantages, features, and details of the invention will become apparent from the following description of a preferred embodiment and from the drawings. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figures, can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the invention.

[0027] The drawing shows:

[0028] Fig. 1 is a schematic representation of an internal combustion engine of a motor vehicle; and

[0029] Fig. 2 is a block diagram illustrating a method for testing a pressure sensor of the internal combustion engine.

[0030] In the figures, identical or functionally identical elements are provided with the same reference symbols.

[0031] Fig. 1 shows a schematic representation of an internal combustion engine 1, also referred to as a motor, internal combustion engine, or internal combustion engine, of a motor vehicle, also simply referred to as a vehicle, which can be driven by the internal combustion engine 1. The internal combustion engine 1, which is designed, for example, as a reciprocating piston engine, i.e. as a reciprocating piston machine, has a plurality of combustion chambers 2. During fired operation of the internal combustion engine 1, respective combustion processes take place in each of them. During each combustion process, a respective fuel-air mixture, also simply referred to as a mixture, is burned, resulting in exhaust gas from the internal combustion engine 1. The exhaust gas can flow out of the respective combustion chamber 2 and into an exhaust tract 3 of the internal combustion engine 1 and subsequently flow through the exhaust tract 3. The respective mixture comprises air and a preferably liquid fuel.In this case, a respective injection valve 4, also referred to as a respective injector, is assigned to the respective combustion chamber 2, by means of which the fuel can be introduced into the respective combustion chamber 2, in this case directly injected.

[0032] The injection valves 4 are components of a fuel system 5 of the internal combustion engine, also referred to as an injection system. The fuel system 5 comprises a fuel distribution element 6 common to the injection valves 4, in which the fuel can be accommodated at least temporarily. The fuel system 5 also comprises a tank 7 in which the fuel can be accommodated or is accommodated. Furthermore, the fuel system 5 comprises a supply line 8, via which the fuel can be fed from the tank 7 to the fuel distribution element 6. The fuel system 5 also comprises a first pump 9 and a second pump 10. In the flow direction of the fuel flowing through the supply line 8, the pump is arranged downstream of the pump 9 and upstream of the fuel distribution element 6.By means of the pump 9, the fuel can be pumped out of the tank 7, towards it, away from itself, and towards the pump 10, which can thus be supplied with the fuel pumped by the pump 9. By pumping the fuel, the pump 9 can create a first fuel pressure, the first pressure of which is also referred to as low pressure. The pump 10 can pump the fuel with which the pump 10 was or is supplied away from itself and towards the fuel distribution element 6, which can thus be supplied with the fuel pumped by the pump 10. By pumping the fuel, the pump 10 can create a second fuel pressure that is greater than the first pressure, the second pressure of which is also referred to as high pressure.Thus, pump 9 is a low-pressure fuel pump, which is also simply referred to as a low-pressure pump, and pump 10 is a high-pressure pump, which is also referred to as a high-pressure fuel pump. The fuel can be held at high pressure, at least temporarily, in the fuel distribution element 6, via which the respective injection valve 4 can be supplied with the high-pressure fuel. Subsequently, the respective injection valve 4 can inject the high-pressure fuel directly into the respective, associated combustion chamber 2. The pump 10 and, for example, also the fuel distribution element 6 and, for example, also the injection valves 4 are, for example, components of a high-pressure region 11 of the fuel system 5, whose high-pressure region 11 is also referred to as the high-pressure system.The pump 9, for example, is part of a low-pressure region 12 of the fuel system 5, whose low-pressure region 12 is also referred to as the low-pressure system. The low-pressure system also includes a first sensor 13, which is designed to detect, i.e., measure, the first fuel pressure prevailing in the low-pressure region 12, also referred to as the low pressure. Therefore, the first sensor 13 is also referred to as a pressure sensor.

[0033] In the exhaust tract 3, a second sensor 14 is arranged in addition to the first sensor 13. This second sensor 14 detects, i.e., measures, a measured variable that characterizes, i.e., describes or indicates, a combustion air ratio of the internal combustion engine 1. The combustion air ratio is or characterizes a composition of the respective mixture. In particular, the sensor 14 is a lambda probe, by means of which a residual oxygen content in the exhaust gas of the internal combustion engine 1 can be detected or is detected, and thus can be or is measured, as the measured variable.

[0034] The following describes a method for testing, i.e., diagnosing, the first sensor 13. The method is carried out by means of an electronic computing device 15 of the internal combustion engine 1 and thus of the motor vehicle.

[0035] Fig. 2 shows a block diagram illustrating the method. In a first step S1 of the method, the measured variable, that is to say in particular the combustion air ratio, is measured by means of the second sensor 14. In a second step S2 of the method, at least one first actual value is determined by means of the electronic computing device 15, which characterizes, that is to say indicates or describes, the measured variable measured by means of the second sensor 14 and thus the combustion air ratio of the internal combustion engine 1. In a third step S3 of the method, a first comparison is carried out by means of the electronic computing device 15, in which the first actual value is compared with a first target value.

[0036] The first comparison is performed, for example, during a mixture diagnosis, during which or based on which the first comparison checks whether the actual value deviates from the first target value. If the first actual value deviates from the first target value, in particular in such a way that the deviation of the first actual value from the first target value exceeds a particularly predeterminable or predetermined threshold value, then, for example, an error in the mixture formation intended to form the respective mixture is detected, i.e., determined.

[0037] In a fourth step S4 of the method, for testing, i.e. for diagnosing the first sensor 18, a diagnosis, also referred to as sensor diagnosis, is carried out by means of the electronic computing device 15, wherein the diagnosis is carried out as a function of a result of the first comparison of the first actual value with the first target value. If, for example, the first comparison determines that the first actual value deviates from the first target value, in particular such that a deviation of the first actual value from the first target value exceeds the stated threshold value, then, for example, and preferably only then, the diagnosis is carried out. However, if, for example, the first comparison determines that the first actual value corresponds to the first target value or that a deviation of the first actual value from the first target value is less than or equal to the stated threshold value, then, for example, the diagnosis still needs to be carried out.

[0038] The diagnosis and thus the fourth step S4 comprise that a second comparison is carried out by means of the electronic computing device 15, in which at least a second actual value, which characterizes, i.e. describes or indicates, the pressure (low pressure) of the fuel measured by the first sensor 13, is compared with a second target value. The diagnosis and thus the fourth step S4 also comprise, for example, that the first sensor 13 is checked as a function of the second comparison of the second actual value with the second target value. For example, it is provided that in a fifth step S5 of the method the motor vehicle, in particular the internal combustion engine 1, is operated as a function of the diagnosis, i.e. in particular as a function of a result of the diagnosis.

[0039] It can be seen that the diagnosis, also referred to as sensor diagnosis, and thus the fourth step S4, depends on the mixture diagnosis. This makes it possible, for example, if a deviation of the first actual value from the first target value is determined based on the first comparison, to reliably, precisely and robustly determine whether or not this deviation of the first actual value from the first target value is due to a fault in sensor 13. If it is determined based on the second comparison that the second actual value corresponds to the second target value or that a deviation of the second actual value from the second target value is less than or equal to a limit that can be predetermined or predefined, then sensor 13, for example, can be ruled out as the cause of the deviation of the first actual value from the first target value.However, if it is determined, for example, based on the second comparison that the second actual value deviates from the second target value or that a deviation of the second actual value from the second target value is greater than the stated limit, the sensor 13 can be determined, for example, as the cause of the deviation of the first actual value from the first target value.

[0040] List of reference symbols

[0041] Internal combustion engine Combustion chamber Exhaust tract Injection valve Fuel system Fuel distribution element Tank

[0042] Supply line first pump second pump high pressure area low pressure area first sensor second sensor electronic computing device first step second step third step fourth step fifth step

Claims

Patent claims 1. A method for testing a first sensor (13) designed to detect a pressure of a fuel intended for operating an internal combustion engine (1), in which: - by means of a second sensor (14) provided in addition to the first sensor (13), a measured variable is measured which characterises a combustion air ratio of the internal combustion engine (19); - at least one first actual value is determined by means of an electronic computing device (15), which characterises the measured variable measured by means of the second sensor (14) and thereby the combustion air ratio of the internal combustion engine (1); - the first actual value is compared with a first target value; - to test the first sensor (13), a diagnosis is carried out which is carried out as a function of a result of the comparison of the first actual value with the first target value; and - the diagnosis comprises: o at least one second actual value, which characterizes the fuel pressure measured by the first sensor (13), is compared with a second target value by means of the electronic computing device (15); and o the first sensor (13) is tested as a function of the comparison of the second actual value with the second target value.

2. Method according to claim 1, characterized in that the same value is always used as the second target value.

3. Method according to claim 1 or 2, characterized in that the second target value is a fixed predetermined value stored in a data memory of the electronic computing device (15) which is retrieved from the data memory.

4. Method according to one of the preceding claims, characterized in that if it is determined based on the comparison of the second actual value with the second target value that the second actual value deviates from the second target value or a deviation of the second actual value from the second target value exceeds a predeterminable or predetermined limit, an error of the first sensor (13) is determined.

5. The method according to claim 4, characterized in that the error is determined as a drift of the first sensor (13).

6. Method according to claim 4 or 5, characterized in that, as a result of the detection of the error, data characterizing the error are stored in an error memory of the electronic computing device (15).

7. Method according to one of the preceding claims, characterized in that, depending on a result of the diagnosis, at least one injection valve (4), by means of which the fuel can be introduced into at least one combustion chamber (2) of the internal combustion engine (1), is operated.

8. Method according to one of the preceding claims, characterized by a pump (9) for conveying the fuel.

9. Method according to claim 8, characterized in that the pump (9) is operated to deliver the fuel depending on a result of the diagnosis.

10. Method according to claim 8 or 9, characterized in that: - a second pump (10) is provided in addition to the pump (9); - by means of the first pump (9) a first pressure of the fuel can be brought about by conveying the fuel and the fuel can be conveyed to the second pump (10), which can be supplied with the fuel having the first pressure; - by means of the second pump (10) while conveying the fuel, a second pressure of the fuel which is higher than the first pressure can be effected and the fuel can be conveyed to at least one component (6) provided in addition to the pumps (9, 10), which component can be supplied with the fuel having the second pressure; and - as the pressure measured by means of the first sensor (13), the first pressure is measured by means of the first sensor (13).

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