Automobile offline engine fault diagnosis method

Abstract

The invention discloses an automobile offline engine fault diagnosis method, and belongs to the technical field of engine detection, and the method comprises the steps: 1, setting a plurality of diagnosis scenes according to the difference of the output power of an engine and the environment temperature, and obtaining the temperature change of the engine in the diagnosis scenes; 2, generating an abnormal index according to the temperature change information of the engine to confirm whether the engine has a fault or not; thirdly, fault marking is conducted on the engine with the fault; step 4, carrying out secondary detection to obtain temperature change during detection; and 5, generating a judgment coefficient according to the obtained temperature change to further diagnose the engine. According to the method, comprehensive analysis is carried out according to the influence of different output power changes on the engine temperature under the same environment temperature and the influence of different environment temperature changes on the engine temperature under the same output power to determine whether the engine temperature has a fault, so that the detection accuracy can be greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of engine detection, and in particular relates to an automobile offline engine fault diagnosis method. Background Art

[0002] The automobile engine is an important part of the automobile, providing power for the automobile. It can be said to be the heart of the automobile. Therefore, its performance and status have an important impact on the overall performance and driving safety of the vehicle. The performance of the automobile engine needs to be tested before it leaves the factory to determine whether there is a performance failure. Generally, offline inspections are mostly manual visual inspections combined with auxiliary tools to test each parameter. For example, when detecting whether the engine has temperature abnormalities, the engine temperature at room temperature is obtained and compared with the standard value. When the ratio exceeds the allowable deviation, the temperature is considered abnormal. Although this method can detect whether the engine temperature is abnormal to a certain extent, due to the influence of changes in ambient temperature and different output powers, the engine temperature changes in different situations will also be different, so it is easy to have errors if only detected by this method. Summary of the invention

[0003] The object of the present invention is to provide a method for diagnosing automobile offline engine faults, so as to solve the problems faced by the above-mentioned background technology.

[0004] The purpose of the present invention can be achieved through the following technical solutions:

[0005] A method for diagnosing an off-line engine fault in an automobile, the method comprising:

[0006] Step 1: setting multiple diagnostic scenarios according to different engine output powers and different ambient temperatures, and obtaining temperature change information of the engine in the diagnostic scenarios;

[0007] Step 2: Analyze and process the acquired engine temperature change information to generate an abnormality index, and confirm whether the engine has a fault based on the abnormality index;

[0008] Step 3: When it is determined that there is a fault, the engine is marked as a fault;

[0009] Step 4: When it is confirmed that there is no fault, the output power of the engine is continuously and slowly increased from low to high at a fixed ambient temperature, and the temperature change of the engine within the increase interval is obtained. At the same time, the ambient temperature is continuously and slowly increased from low to high at a fixed output power, and the temperature change of the engine within the increase interval is obtained;

[0010] Step 5: Further analyze and process the acquired temperature change information to generate a judgment coefficient, and perform a secondary detection on whether the engine has a fault based on the size of the judgment coefficient.

[0011] Furthermore, the method for confirming whether the engine has a fault according to the abnormality index in step 2 is:

[0012] Get the first abnormal index fle at a fixed ambient temperature b , get the second abnormal index fle under fixed output power c ;

[0013] Thus, through the formula fl e = a1 * fl e b +a2*fle c The abnormal index fle is obtained;

[0014] The abnormal index fle is compared with the preset abnormal index threshold fle ts To compare:

[0015] When fle>fle ts When , it is considered that the engine is faulty, where a1 and a2 are proportional coefficients.

[0016] Furthermore, the first abnormality index fle b The acquisition method is:

[0017] At a fixed ambient temperature, x diagnostic intervals are set according to the size of the engine output power. In each diagnostic interval, the engine operates at a fixed output power, and the temperature variation curve Tb in each diagnostic interval is obtained. i (t), so through the formula Get the first change value Rb of each diagnostic interval i ;

[0018] According to the relationship between the first change value Rb and the diagnostic interval x, a curve equation f(x Rb) between the first change value and the diagnostic interval is constructed, so that the formula Get the first abnormal index fle b ;

[0019] in, And i∈(1,x), f0(x Rb) is the standard curve equation between the preset first change value and the diagnostic interval, t a is the start time of the diagnostic interval, t b is the end time of the diagnostic interval, is the standard curve of temperature variation over time in the i-th diagnostic interval.

[0020] Furthermore, the second abnormality index fle c The acquisition method is:

[0021] Under fixed output power, according to different ambient temperatures, y diagnostic intervals are set. The ambient temperature in each diagnostic interval is fixed, and the temperature variation curve Tc in each diagnostic interval is obtained. j (t), so through the formula Get the second change value Rc of each diagnostic interval j , and construct the curve equation f(y Rc) between the second change value and the diagnostic interval, so that the formula The second abnormal index fle c ;

[0022] in, And j∈(1, y), f0(y Rc) is the standard curve equation between the preset second change value and the diagnostic interval, t x is the start time of the diagnostic interval, t y is the end time of the diagnostic interval, is the standard curve of temperature variation over time in the jth diagnostic interval.

[0023] Furthermore, the method for generating the judgment coefficient in step 5 is:

[0024] Under a fixed ambient temperature, obtain the curve Tem(P) of the engine temperature changing with the output power P, and at the same time, obtain the curve Tem(AT) of the engine temperature changing with the ambient temperature AT under a fixed output power;

[0025] So through the formula The judgment coefficient TF is obtained;

[0026] Among them, P1 is the output power at the beginning, P2 is the output power at the end, Tem0(P) is the preset standard curve of engine temperature changing with power, AT1 is the ambient temperature at the beginning, AT2 is the ambient temperature at the end, Tem0(AT) is the preset standard curve of engine temperature changing with ambient temperature, AP and ΔAT are the respective change comparison reference values.

[0027] Furthermore, the method of secondary detection in step 5 is:

[0028] The obtained judgment coefficient TF is compared with the preset judgment threshold coefficient TF ts To compare:

[0029] When TF>TF ts When the engine is faulty, it is judged that the engine is faulty and a fault mark is performed;

[0030] Otherwise, the engine is judged to be normal.

[0031] Furthermore, the diagnostic method further includes performing a quality rating on the engine judged to be normal;

[0032] When it is determined that no fault occurs in the second engine inspection, the abnormal index fle of the engine during the first inspection and the judgment coefficient TF during the second inspection are obtained;

[0033] When 3 fl e+2 TF ∈[2, Q1], it is judged as excellent;

[0034] When 3 fle +2 TF ∈(Q1, +∞), it is judged as qualified;

[0035] Where Q1 is the preset quality assessment threshold.

[0036] Beneficial effects of the present invention:

[0037] The present invention sets a plurality of diagnostic scenarios according to the different engine output powers and the different ambient temperatures. A comprehensive analysis can be performed based on the influence of different output power changes on the engine temperature at the same ambient temperature and the influence of different ambient temperature changes on the engine temperature at the same output power to determine whether there is a fault in the engine temperature. This can greatly improve the accuracy of detection and reduce the errors in detection.

[0038] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0040] Figure 1 The present invention is a flow chart of the method. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] In one embodiment, a method for diagnosing an off-line engine fault in an automobile is disclosed. Figure 1 As shown, diagnostic methods include:

[0043] Step 1: setting multiple diagnostic scenarios according to different engine output powers and different ambient temperatures, and obtaining temperature change information of the engine in the diagnostic scenarios;

[0044] Step 2: Analyze and process the acquired engine temperature change information to generate an abnormality index, and confirm whether the engine has a fault based on the abnormality index;

[0045] Step 3: When it is determined that there is a fault, the engine is marked as a fault;

[0046] Step 4: When it is confirmed that there is no fault, the output power of the engine is continuously and slowly increased from low to high at a fixed ambient temperature, and the temperature change of the engine within the increase interval is obtained. At the same time, the ambient temperature is continuously and slowly increased from low to high at a fixed output power, and the temperature change of the engine within the increase interval is obtained;

[0047] Step 5: Further analyze and process the acquired temperature change information to generate a judgment coefficient, and perform a secondary detection on whether the engine has a fault based on the size of the judgment coefficient.

[0048] Through the above technical scheme, the present application sets multiple diagnostic scenarios according to the different engine output power and the different ambient temperature, and comprehensively analyzes the engine temperature changes corresponding to different output power sizes at a fixed ambient temperature, and the engine temperature changes corresponding to different ambient temperatures under a fixed output power, to obtain an abnormal index, and first diagnoses whether the engine has a fault problem according to the size of the abnormal index, so as to mark the engine with the fault; then, when it is confirmed that there is no fault, the engine output power is slowly and continuously increased from low to high at a fixed ambient temperature, and the temperature change of the engine within the increase interval is obtained, and the ambient temperature is slowly and continuously increased from low to high at a fixed output power, and the temperature change of the engine within the increase interval is obtained, and the temperature change is analyzed and processed in combination with the temperature change, so as to generate a judgment coefficient, and a secondary detection is performed on whether the engine has a fault according to the size of the judgment coefficient, and the engine diagnosed with a fault problem is marked. In this way, the influence of different output power changes at the same ambient temperature on the engine temperature and the influence of different ambient temperature changes at the same output power on the engine temperature can be combined to perform a comprehensive analysis to determine whether the engine temperature has a fault, which can greatly improve the accuracy of monitoring.

[0049] As an implementation mode of the present invention, the method for confirming whether the engine has a fault according to the size of the abnormality index in step 2 is:

[0050] Get the first abnormal index fle at a fixed ambient temperature b , get the second abnormal index fle under fixed output power c ;

[0051] Thus, through the formula fl e = a1 * fl e b +a2*fle c The abnormal index fle is obtained;

[0052] The abnormal index fle is compared with the preset abnormal index threshold fle ts To compare:

[0053] When fle>fle ts When , it is considered that the engine is faulty, where a1 and a2 are proportional coefficients;

[0054] The first abnormal index fle b The acquisition method is: under a fixed ambient temperature, according to the size of the engine output power, set x diagnostic intervals, the engine operates at a fixed output power in each diagnostic interval, and obtain the temperature change curve Tb in each diagnostic interval i (t), so through the formula Get the first change value Rb of each diagnostic interval i ;

[0055] According to the relationship between the first change value Rb and the diagnostic interval x, a curve equation f(x Rb) between the first change value and the diagnostic interval is constructed, so that the formula Get the first abnormal index fle b ;

[0056] in, And i∈(1,x), f0(x Rb) is the standard curve equation between the preset first change value and the diagnostic interval, t a is the start time of the diagnostic interval, t b is the end time of the diagnostic interval, is the standard curve of temperature variation over time in the i-th diagnostic interval;

[0057] The second abnormal index fle c The acquisition method is: under a fixed output power, according to the different ambient temperatures, set y diagnostic intervals, the ambient temperature in each diagnostic interval is fixed, and the temperature change curve Tc in each diagnostic interval is obtained. j (t), so through the formula Get the second change value Rc of each diagnostic interval j, and construct the curve equation f(y Rc) between the second change value and the diagnostic interval, so that the formula The second abnormal index fle c ;

[0058] in, And j∈(1, y), f0(y Rc) is the standard curve equation between the preset second change value and the diagnostic interval, t x is the start time of the diagnostic interval, t y is the end time of the diagnostic interval, is the standard curve of temperature variation over time in the jth diagnostic interval.

[0059] Through the above technical solution, this embodiment provides a method for generating an abnormality index and a specific method for confirming whether an engine has a fault according to the abnormality index. First, a first abnormality index fle is obtained. b : Under a fixed ambient temperature, x diagnostic intervals are set according to the size of the engine output power. In each diagnostic interval, the engine operates at a fixed output power, and the temperature variation curve Tb in each diagnostic interval is obtained. i (t), so through the formula Get the first change value Rb of each diagnostic interval i , set a fixed ambient temperature, give different output powers in each diagnostic interval, to obtain the temperature change curve Tb in each diagnostic interval i (t), and compared with the set temperature change over time standard curve. It can be seen from the formula that when the first change value Rb is smaller, the difference between the temperature change and the standard temperature change is smaller, which means that the possibility of temperature failure of the engine is smaller. Then, according to the relationship between the first change value Rb and the diagnostic interval x, the curve equation f(x Rb) between the first change value and the diagnostic interval is constructed, so that the formula Get the first abnormal index fle b , it can be seen from the formula that the formula It represents the fluctuation of the engine temperature change value in the entire diagnostic scenario. The smaller the value, the better the engine performance. The formula It indicates the difference between the temperature change value and the standard temperature change value in the entire diagnostic scenario. The smaller the value, the better the engine performance. Therefore, when the first abnormal index fle b The smaller the value, the smaller the possibility of engine failure; then obtain the second abnormality index fle c: Under fixed output power, according to different ambient temperatures, y diagnostic intervals are set. The ambient temperature in each diagnostic interval is fixed, and the temperature variation curve Tc in each diagnostic interval is obtained. j (t), so through the formula Get the second change value Rc of each diagnostic interval j , and construct the curve equation f(y Rc) between the second change value and the diagnostic interval, so that the formula The second abnormal index fle c ; So in the first abnormal index fle b And the second abnormal index fle c Then, through the formula fl=a1*fle b +a2*fle c Comprehensive analysis is performed to obtain the abnormal index fle; it can be seen that the smaller the value of the abnormal index, the smaller the risk of engine failure, so an abnormal index threshold fle is preset based on historical experience data ts , compare the abnormal index fle with the preset abnormal index threshold fle ts Compare: When fle>fle ts When the abnormal index threshold is too large, it is considered that the engine has a temperature fault, otherwise it indicates that the engine does not have a temperature fault. In this way, a comprehensive analysis can be performed based on the impact of different output power changes on the engine temperature at the same ambient temperature and the impact of different ambient temperature changes on the engine temperature at the same output power to determine whether the engine temperature has a fault, which can greatly improve the accuracy of detection.

[0060] In the above technical solution, the standard curve equation between the preset first change value and the diagnostic interval is f0(x Rb), the standard curve equation between the preset second change value and the diagnostic interval is f0(y Rc), and the standard curve of temperature change over time in the diagnostic interval is as well as Both can be formulated based on the analysis of data of the same engine in related scenarios under big data. The diagnostic interval can be formulated by humans based on actual conditions, and the proportional coefficients a1 and a2 are determined based on empirical data.

[0061] As an implementation of the present invention, the method for generating the judgment coefficient in step 5 is:

[0062] Under a fixed ambient temperature, obtain the curve Tem(P) of the engine temperature changing with the output power P, and at the same time, obtain the curve Tem(AT) of the engine temperature changing with the ambient temperature AT under a fixed output power;

[0063] So through the formula The judgment coefficient TF is obtained;

[0064] Wherein, P1 is the output power at the beginning, P2 is the output power at the end, Tem0(P) is the preset standard curve of engine temperature changing with power, AT1 is the ambient temperature at the beginning, AT2 is the ambient temperature at the end, Tem0(AT) is the preset standard curve of engine temperature changing with ambient temperature, AP and ΔAT are the respective reference values ​​for change comparison;

[0065] The method of the secondary detection in step 5 is: the obtained judgment coefficient TF is compared with the preset judgment threshold coefficient TF ts To compare:

[0066] When TF>TF ts When the engine is faulty, it is judged that the engine is faulty and a fault mark is performed;

[0067] Otherwise, the engine is judged to be normal.

[0068] Through the above technical solution, the present application provides another method for diagnosing engine faults. Since the above-mentioned diagnostic method is configured such that the output power or ambient temperature within the diagnostic interval is detected at a fixed value, the present embodiment adjusts the output power and ambient temperature within the diagnostic interval to obtain the engine temperature variation curve Tem(P) with the output power P at a fixed ambient temperature, and the engine temperature variation curve Tem(AT) with the ambient temperature AT at a fixed output power, thereby obtaining the engine temperature variation curve Tem(P) with the ambient temperature AT at a fixed output power, and then obtaining the engine temperature variation curve Tem(AT ... ambient temperature, and then obtaining the engine temperature variation curve Tem(AT) with the ambient temperature AT at a fixed ambient temperature, and then obtaining the engine temperature variation curve Tem(P) with the output power P at a fixed ambient temperature, and then obtaining the engine temperature variation curve Tem(AT) with the output power P at a fixed ambient temperature, and then obtaining the engine temperature variation curve Tem(AT) with the output power P at a fixed ambient temperature, and then obtaining the engine temperature variation curve Tem(P) with the output power P at a fixed ambient temperature, and then obtaining the engine temperature variation curve Tem(AT) with the output power P at a fixed ambient temperature, and then obtaining the engine temperature variation curve Tem(AT) with the output power P at a fixed ambient temperature, and then obtaining the engine temperature variation curve Tem(P) with the output power P at a fixed ambient temperature, and then obtaining the engine temperature variation curve Tem(AT) with the output power P at a fixed ambient temperature, and then obtaining the engine temperature variation curve T The judgment coefficient TF is obtained, the formula It indicates the difference between the obtained temperature change with output power and the preset engine temperature change with output power standard. The smaller the difference between the two, the smaller the possibility of engine failure. The same formula It indicates the difference between the obtained temperature change with the ambient temperature and the preset engine temperature change with the ambient temperature standard. The smaller the difference between the two, the smaller the possibility of engine failure. Therefore, the formula Combine the two for comprehensive analysis to get the judgment coefficient. According to the size of the judgment coefficient, it is judged whether the engine has temperature abnormality. Specifically, the obtained judgment coefficient TF is compared with the preset judgment threshold coefficient TF. ts Compare: When TF>TF ts If the temperature of the engine is abnormal, the engine temperature is judged to be normal. In this way, the influence of the change of ambient temperature and the change of output power on the engine temperature can be used to more accurately judge the abnormal engine temperature.

[0069] In the above technical solution, the initial change of output power and the initial change of ambient temperature can be determined according to the actual situation. The preset standard curve of engine temperature changing with power Tem0(P) and the preset standard curve of engine temperature changing with ambient temperature Tem0(AT) can be formulated based on the analysis of data of the same engine in relevant scenarios under big data. The respective changes are compared with the reference values ​​ΔP and ΔAT, and the preset judgment threshold coefficient TF. ts Determined based on empirical data.

[0070] As an embodiment of the present invention, the diagnostic method further includes performing a quality rating on the engine determined to be normal;

[0071] When it is determined that no fault occurs in the second engine inspection, the abnormal index fle of the engine during the first inspection and the judgment coefficient TF during the second inspection are obtained;

[0072] When 3 fl e+2 TF ∈[2, Q1], it is judged as excellent;

[0073] When 3 fl e+2 TF ∈(Q1, +∞), it is judged as qualified;

[0074] Where Q1 is the preset quality assessment threshold.

[0075] Through the above technical solution, this embodiment provides a method for rating the quality of an engine judged to be normal. When it is judged that the engine has no fault after two tests, the abnormal index fle of the engine during the first test and the judgment coefficient TF during the second test are obtained, and then compared with the preset quality assessment threshold Q1. The preset quality assessment threshold Q1 is determined based on empirical data. If the abnormal index and the judgment coefficient are both small, it means that the possibility of temperature failure of the engine is small, that is, when 3 fle +2 TF ∈[2, Q1], the engine quality is judged to be excellent. fle +2 TF ∈(Q1, +∞), it means that the possibility of temperature failure of the engine is higher than the former one, and it is judged as qualified; similarly, the unqualified engine failure can also be analyzed in this way to determine the level of unqualified, so as to facilitate subsequent maintenance and improvement.

[0076] It should be noted that the calculation formulas and various parameters involved in the calculations in the present invention have been dimensionally processed in advance, and the process of dimensionless processing is well known in the industry and will not be described here.

[0077] The above contents are merely examples and explanations of the concept of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. A method for diagnosing an off-line engine fault in an automobile, characterized in that: The diagnostic method comprises: Step 1: setting multiple diagnostic scenarios according to different engine output powers and different ambient temperatures, and obtaining temperature change information of the engine in the diagnostic scenarios; Step 2: Analyze and process the acquired engine temperature change information to generate an abnormality index, and confirm whether the engine has a fault based on the abnormality index; Step 3: When it is determined that there is a fault, the engine is marked as a fault; Step 4: When it is confirmed that there is no fault, the output power of the engine is continuously and slowly increased from low to high at a fixed ambient temperature, and the temperature change of the engine within the increase interval is obtained. At the same time, the ambient temperature is continuously and slowly increased from low to high at a fixed output power, and the temperature change of the engine within the increase interval is obtained; Step 5: Further analyze and process the acquired temperature change information to generate a judgment coefficient, and perform a secondary detection on whether the engine has a fault based on the size of the judgment coefficient.

2. The method for diagnosing an off-line engine fault in an automobile according to claim 1, characterized in that: The method for confirming whether the engine has a fault according to the abnormal index in step 2 is: Get the first abnormal index fle at a fixed ambient temperature b , get the second abnormal index fle under fixed output power c ; Thus, through the formula fl e = a1 * fl e b +a2*fle c The abnormal index fle is obtained; The abnormal index fle is compared with the preset abnormal index threshold fle ts To compare: When fle>fle ts When , it is considered that the engine is faulty, where a1 and a2 are proportional coefficients.

3. The method for diagnosing an off-line engine fault in an automobile according to claim 2, characterized in that: The first abnormal index fl b The acquisition method is: At a fixed ambient temperature, x diagnostic intervals are set according to the size of the engine output power. In each diagnostic interval, the engine operates at a fixed output power, and the temperature variation curve Tb in each diagnostic interval is obtained. i (t), so through the formula Get the first change value Rb of each diagnostic interval i ; According to the relationship between the first change value Rb and the diagnostic interval x, a curve equation f(x Rb) between the first change value and the diagnostic interval is constructed, so that the formula Get the first abnormal index fle b ; in, And i∈(1,x), f0(x Rb) is the standard curve equation between the preset first change value and the diagnostic interval, t a is the start time of the diagnostic interval, t b is the end time of the diagnostic interval, is the standard curve of temperature variation over time in the i-th diagnostic interval.

4. The method for diagnosing an off-line engine fault in an automobile according to claim 2, characterized in that: The second abnormal index fl c The acquisition method is: Under fixed output power, according to different ambient temperatures, y diagnostic intervals are set. The ambient temperature in each diagnostic interval is fixed, and the temperature variation curve Tc in each diagnostic interval is obtained. j (t), so through the formula Get the second change value Rc of each diagnostic interval j , and construct the curve equation f(y Rc) between the second change value and the diagnostic interval, so that the formula The second abnormal index fle c ; in, And j∈(1, y), f0(y Rc) is the standard curve equation between the preset second change value and the diagnostic interval, t x is the start time of the diagnostic interval, t y is the end time of the diagnostic interval, is the standard curve of temperature variation over time in the jth diagnostic interval.

5. The method for diagnosing an off-line engine fault in an automobile according to claim 1, characterized in that: The method for generating the judgment coefficient in step 5 is: Under a fixed ambient temperature, obtain the curve Tem(P) of the engine temperature changing with the output power P, and at the same time, obtain the curve Tem(AT) of the engine temperature changing with the ambient temperature AT under a fixed output power; So through the formula The judgment coefficient TF is obtained; Among them, P1 is the output power at the beginning, P2 is the output power at the end, Tem0(P) is the preset standard curve of engine temperature changing with power, AT1 is the ambient temperature at the beginning, AT2 is the ambient temperature at the end, Tem0(AT) is the preset standard curve of engine temperature changing with ambient temperature, ΔP and ΔAT are respective reference values ​​for change comparison.

6. The method for diagnosing an off-line engine fault in an automobile according to claim 5, characterized in that: The method of secondary detection in step 5 is: The obtained judgment coefficient TF is compared with the preset judgment threshold coefficient TF ts To compare: When TF>TF ts When the engine is faulty, it is judged that the engine is faulty and a fault mark is performed; Otherwise, the engine is judged to be normal.

7. The method for diagnosing an off-line engine fault in an automobile according to claim 6, characterized in that: The diagnostic method further includes performing a quality rating on the engine determined to be normal; When it is determined that no fault occurs in the second engine inspection, the abnormal index fle of the engine during the first inspection and the judgment coefficient TF during the second inspection are obtained; When 3 fle +2 TF ∈[2, Q1], it is judged as excellent; When 3 fle +2 TF ∈(Q1, +∞), it is judged as qualified; Where Q1 is the preset quality assessment threshold.

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