JP2632618B2 - Fault diagnosis method for vehicles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for diagnosing a failure in a vehicle, and more particularly to a method for diagnosing a failure based on a result of communication with a vehicle-mounted electronic control unit (hereinafter referred to as an ECU) mounted on the vehicle. The present invention relates to a failure diagnosis method for vehicles.

[0002]

2. Description of the Related Art In recent years, automobiles and motorcycles (hereinafter, referred to as vehicles) have been developed in order to improve engine control functions.
The engine ignition timing control, valve opening / closing timing control, fuel injection control by an electronic fuel injection device (EFI), and the like, are increasingly performed by a vehicle-mounted electronic control device (ECU) having a microcomputer. .

The ECU includes a pressure sensor for detecting a negative pressure of an air suction pipe, a temperature sensor for detecting a temperature of engine cooling water, a rotation sensor for detecting an engine speed, and an O2 sensor for detecting an oxygen concentration in exhaust gas. Various sensors such as sensors are connected, and the ECU performs various controls based on detection signals output from the various sensors.

The ECU has a self-diagnosis function. When an abnormal signal outside the reference range is detected, the ECU determines that a failure has occurred, and stores in a memory a failure code for identifying a location where the abnormal signal was output and a value of the abnormal signal. I do.

[0005] In a vehicle equipped with such an ECU, a failure diagnosis device is prepared which is used by connecting to the ECU at a maintenance shop or the like. In this failure diagnosis device, a failure diagnosis program for discovering the contents of the failure is registered.

The failure diagnosis device communicates with the ECU according to the failure diagnosis program, determines a failure location from the communication result, and displays the failure location on a display (LCD). If it is determined that there are a plurality of failure points, the LC
D indicates all the failure points. The repair staff can easily confirm the failure location based on this display, and can take appropriate measures promptly.

[0007]

However, the above-described conventional fault diagnosis apparatus cannot diagnose a fault, such as a broken wire or a short circuit, in which a fault location and a fault state can be quantitatively detected. Was.

That is, when the voltage of the system input to a certain sensor is, for example, DC 5 [V], when the sensor is normal, the output voltage is, for example, 0.05 to 0.05.
4.95 [V]. When the sensor is short-circuited to the ground side and when the sensor has a disconnection fault, 0.05
[V] or less, and 4.95 [V] or more.

Therefore, by detecting the output voltage of the sensor, it is possible to easily diagnose which sensor (fault location) and how (disconnection or short circuit; failure state) are defective.

However, a direct signal input from the outside
Depending on the behavior can not be changed, the behavior
Environment, operation, <br/> fault condition to effect changes under the condition such that it is difficult to capture quantitatively "external signal response
There is a problem that the failure diagnosis is difficult for the failure of the “unanswerable part” .

[0011] Hereinafter, the failure of the external signal unresponsive site was determined (1) the air-fuel ratio of the mixture (air volume / fuel amount)
Deterioration of the "O2 sensor" for detecting the oxygen concentration in the exhaust gas , and (2) recirculation of the exhaust gas to the combustion chamber of the engine "E
A description will be given by taking a failure of the GR as an example.

FIG. 1 is a configuration diagram of an intake and exhaust system of an engine for explaining the functions of an O2 sensor and EGR .

The engine 73 is connected to an inlet manifold 75 for supplying a fuel gas and an outlet manifold 74 for exhausting the burned gas.
A throttle valve 76 is incorporated in the inlet manifold 75, and the throttle valve 76 is opened and closed by an accelerator operation, thereby controlling the engine speed.

The inlet manifold 75 includes:
EACV bypassing upstream and downstream of throttle valve 76
70 are connected. The EACV 70 adds fuel gas to the engine 73 to increase the engine speed when a load is applied to the engine such as when the engine is started, when the engine is warm, when the cooler is operating, or when an electrical load is applied. The solenoid valve is a solenoid valve for supplying fuel gas to the fuel cell, and includes a bypass passage 77 for bypassing the fuel gas, a bypass valve 78 for limiting the flow rate of the fuel gas, and a solenoid 71 for controlling the opening of the bypass valve 78.

The flow rate of the fuel gas bypassed by the EACV 70 is continuously controlled by varying the amount of current supplied from the EACV drive circuit 72 to the coil 79 of the solenoid 71 in accordance with the load indicated by the ECU 1.

On the other hand, an outlet manifold 75 downstream of the outlet manifold 74 and the throttle valve 76
a is connected via the EGR 50.

The EGR 50 is an exhaust gas recirculation device for reducing NOx by recirculating exhaust gas into the combustion chamber of the engine and reburning unburned gas. The EGR 50 includes a first body 52 having a control port 51 and a first body 52 having a control port 51. , Atmospheric port 5
3, a second body 56 having an intake port 54 and an exhaust port 55.

The first body 52 and the second body 56 are separated by a diaphragm 57. Diaphragm 57
A compression coil spring 58 that pushes this toward the second body 56, and a diaphragm 57
, The other end of which faces the exhaust port 55
Is provided.

The displacement of the valve body 59 is detected by a lift sensor 61. The second body 56 is provided with a partition wall 60 for partitioning the inside between the atmosphere port 53 and the intake port 54.

The lift sensor 61 is connected to the ECU 1. The control port 51 is connected to an inlet manifold 75 through an electromagnetic valve 82 whose valve opening is controlled by the ECU 1.
It is connected to.

The amount of exhaust gas circulated by the EGR 50 (EG
R amount) depends on the opening degree of the valve body 59, so the ECU 1 obtains the EGR amount based on the position signal of the valve body 59 given by the lift sensor 61. Increase the opening. As a result, the negative pressure of the control port 51 increases, and the diaphragm 57 resists the first body 5 against the repulsive force of the compression coil spring 58.
2 so that the exhaust port 55
The amount of EGR flowing to is increased.

An O2 sensor 83 is provided downstream of the outlet manifold 74 and its output signal is
It is input to U1. The ECU 1 obtains an air-fuel ratio based on a detection signal from the O2 sensor 83, and controls a fuel injection amount by an injector (not shown) so as to obtain an optimum air-fuel ratio.

Hereinafter, the causes of failure of each unit will be described. (1) The relationship between the air-fuel ratio of the deteriorated air-fuel mixture of the O2 sensor and the output voltage of the O2 sensor is as shown in FIG. At present, the ideal air-fuel ratio is said to be 14.7, and the output voltage of the O2 sensor rapidly changes near the air-fuel ratio of 14.7. If the output voltage of the O2 sensor is high, the fuel supply amount is decreased, and if the output voltage of the O2 sensor is low, the fuel supply amount is increased. As a result, under the air-fuel ratio control based on the output voltage of the O2 sensor, the output voltage of the O2 sensor has a waveform as shown in FIG.

On the other hand, when the O2 sensor is deteriorated, the output voltage fluctuates slowly (that is, the frequency decreases) with respect to the change in the air-fuel ratio, or the amplitude range of the output signal (the difference between the maximum value and the minimum value; P −P) becomes smaller, so that an optimal air-fuel ratio cannot be maintained and drivability is reduced.

However, since it is difficult to quantitatively measure such a variation in the frequency or the variation in the amplitude range with a simple configuration, it has not been possible to detect the deterioration of the O2 sensor by the failure diagnosis device. could not. (2) EGR Failure The malfunction of the valve body 59 of the EGR 50 can be detected by referring to the position signal from the lift sensor 61. However, the malfunction of the valve body 59 is not necessarily caused by the failure of the EGR 50, It is also caused by a failure of the valve 82.

In other words, even if the valve element 59 does not operate, the direct cause of the non-operation cannot be determined based on the quantitative detection value from the lift sensor 61. It was difficult to detect with a diagnostic device.

It is an object of the present invention to solve the above-mentioned problems of the prior art and to provide a failure diagnosis method capable of diagnosing a failure in which it is difficult to quantitatively determine a failure location and a failure state.

[0028]

According to the present invention, there is provided a vehicle failure diagnosis method for diagnosing a failure in a portion where it is difficult to quantitatively determine a failure location and a failure state. A known state is created by an external signal input, a quantitative inspection result obtained at this time is compared with a result predicted from the known state, and failure diagnosis of each part is performed based on the comparison result. I did it.

[0029]

When a signal for bringing a diagnosis target into a known state is input from the outside, if the diagnosis target is normal, a test result obtained from the diagnosis target is a result predicted from the known state. If the diagnosis target is not normal, the predicted result is not obtained. Therefore, a comparison between the test result in a known state and the predicted result makes it possible to perform a failure diagnosis.

[0030]

FIG. 2 is a block diagram of an ECU of a vehicle to be diagnosed and a failure diagnosis device connected to the ECU according to an embodiment of the present invention.

Referring to FIG. 1, the ECU 1 includes a CPU 10,
It comprises a ROM 11, a RAM 12, a driver 13, an A / D converter 14, and a communication interface 15. This ECU 1 is connected to peripheral devices via connectors 16 and 17. The connector 18 is connected to a failure diagnosis device 2 described later.

Various actuators 3 are connected to the connector 16.
Are connected, and various sensors 4 are connected to the connector 17. The ECU 1 performs ignition timing control, EFI control, and the like. For example, when performing EFI control, a solenoid is connected as the actuator 3 to the connector 16, and a TDC sensor, a water temperature sensor as the sensor 4 is connected to the connector 17. , An intake air temperature sensor, a throttle valve opening sensor, and the like.

A signal input from each sensor 4 to the ECU 1 is converted into a digital signal by an A / D converter
Taken in U10. The signal taken into the CPU 10 is
Based on the control data stored in the ROM 11 and the RAM 12, processing is performed according to a program written in the ROM 11. An instruction signal corresponding to the processing result of the CPU 10 is input to the driver 13, and the driver 13 supplies power to the actuator 3 in response to the instruction signal.

The ROM 11 also registers, in addition to the program, an identification code of the ECU 1, that is, an ECU-ID. Further, the processing result of the CPU 10 is stored in the RAM 12 as learning data or freeze data. This freeze data is data representing the operating state of the engine when a malfunction occurs.

A failure diagnosis device 2 connected to the ECU 1 for performing a failure diagnosis of the ECU 1 includes a CPU 20, a R
OM21, RAM22, driver 23, A / D converter 2
4 and a communication interface 25. In addition, the display unit 27 for displaying the result of processing by the keyboard 26, and CPU20 for inputting an instruction by the operator is provided in the fault diagnosis apparatus 2. The keyboard 26 is provided with general numeric keys, cursor movement keys, function keys, and the like. The display unit 2
As 7, a liquid crystal display panel (LCD) can be employed.

A test probe 6 is connected to the failure diagnosis device 2 to realize a voltage / resistance measurement function as a tester function and a test signal (constant voltage signal) output function.
That is, when a voltage output from the driver 23 is supplied to the test probe 6, a test signal (a reference value described later) of the sensor 4 can be output from the test probe 6. On the other hand, the signal detected by the test probe 6 is
The signal is converted into a digital signal by the A / D converter 24 and
It is taken into 0.

The communication interface 15 of the ECU 1 and the communication interface 25 of the failure diagnosis device 2 are connected via the cable 5 so that bidirectional digital communication can be performed between the CPUs 10 and 20.

The signal received from the ECU 1 and the signal obtained by the test probe 6 are stored in the ROM 21 and the RAM
Processing is performed based on the control data stored in the storage unit 22, and a processing result, that is, a failure diagnosis result is output to the display unit 27. A failure diagnosis program for specifying a failure location is registered in the ROM 21.

Further, the ROM 21 stores a selection program for selecting an optimum one from a plurality of failure diagnosis programs based on the ECU-ID and the failure information. In addition, with the production of a new model, a failure diagnosis program may be added or changed. For such a case, the failure diagnosis program and the selection program
The data may be stored in the OM card 7 and the data of the ROM card 7 may be taken into the CPU 20 from the ROM card interface 28.

It is also possible to connect the failure diagnosis device 2 to a personal computer (not shown), accumulate the failure diagnosis results in this personal computer, and print out the results as necessary. Further, the personal computer can be connected to a host computer via a public line, and a failure diagnosis result can be supplied to the host computer. Conversely, the host computer may provide the personal computer and the failure diagnosis device 2 with necessary information, for example, updated (upgraded) versions of the failure diagnosis program and the selection program. it can.

It is desirable that the failure diagnosis device 2 has a built-in battery as a power source so that it can be carried away from the repair shop. This battery can be supplied with power from a vehicle battery via a socket of a writer. And a rechargeable battery such as a Ni-Cd battery.

Hereinafter, the failure diagnosis method of the present invention will be described with reference to a flowchart. The operation described below is executed in a state where the failure diagnosis device 2 is connected to the ECU 1 of the vehicle. Further, in each flowchart, a process surrounded by a broken line indicates a process performed by a repair worker of the failure diagnosis device 2.

FIG. 5 shows an EGR according to a first embodiment of the present invention.
5 is a flowchart showing a failure diagnosis method of FIG.

When the failure diagnosis is started, step S10
In step 1, the failure diagnostic device 2 outputs an instruction to the ECU 1 to forcibly close the electromagnetic valve 82 to the ECU 1.
U1 closes the electromagnetic valve 82 according to the instruction.

In step S102, an instruction to detect the output signal of the lift sensor 61 is output from the failure diagnosis device 2 to the ECU 1, and the ECU 1
1, the position of the valve body 59 is detected.

In step S103, the failure diagnosis device 2 determines the open / closed state of the EGR based on the detection result by the ECU 1, and operates when the EGR is open even though the engine is stopped and no negative pressure is generated. It is determined to be defective, and the process proceeds to step S104.

In step S104, an instruction to disconnect the pipe from the control port 51 of the EGR is displayed on the display unit 27 of the failure diagnosis device 2.

The repair worker removes the piping and removes the failure diagnosis device 2
Is pressed, in step S105,
The failure diagnostic device 2 sends a lift sensor 6 to the ECU 1.
An instruction to detect the output signal of the ECU 1 is output.
Detects the position of the valve element 59 based on the output signal of the lift sensor 61.

In step S106, the failure diagnosis device 2 determines the open / closed state of the EGR based on the detection result by the ECU 1, and the failure diagnosis device 2 determines that the EGR is open, that is, "EGR failure". At
The determination result is displayed on the display unit 27. Further, if the EGR is in the closed state, it is determined that "the solenoid valve is defective", and step S108 is performed.
In, the determination result is displayed on the display unit 27.

In step S103, E
If it is determined that the GR is in the closed state, step S109
Then, a work instruction to start the engine is displayed on the display unit 27 of the failure diagnosis device 2, and the repair worker starts the engine.

In step S110, an instruction to detect the output signal of the lift sensor 61 is again output from the failure diagnosis device 2 to the ECU 1, and the ECU 1 determines the position of the valve body 59 based on the output signal of the lift sensor 61. Is detected.

In step S111, the failure diagnosis device 2 determines the open / closed state of the EGR based on the detection result by the ECU 1, determines that the EGR is in the open state, and determines that the EGR is malfunctioning. The process proceeds to the step S104. The same diagnostic processing as described above is executed.

If it is determined that the EGR is in the closed state, the process proceeds to step S112 where the failure diagnosis device 2
The ECU 1 outputs an instruction to forcibly open the electromagnetic valve 82 to the electromagnetic valve 8.
Open 2.

In step S113, an instruction to detect the output signal of the lift sensor 61 is output from the failure diagnostic device 2 to the ECU 1 again, and the ECU 1 determines the position of the valve body 59 based on the output signal of the lift sensor 61. Is detected.

In step S114, the failure diagnosis device 2 determines whether the EGR is open or closed based on the detection result of the ECU 1. If the EGR is in the closed state, it determines that the EGR or the solenoid valve is defective. Is displayed on the display unit 27.

If the EGR is in the open state, it is determined that the EGR is in the normal state, and the result of the determination is displayed on the display unit 27 in step S115.

FIG. 6 shows an EG according to a second embodiment of the present invention.
FIG. 7 is a flowchart showing a failure diagnosis method for R, and FIG.
FIG. 4 is a diagram showing the contents of diagnosis by the failure diagnosis method.

When the failure diagnosis is started, step S20
In step 1, the failure diagnostic device 2 outputs an instruction to the ECU 1 to forcibly close the electromagnetic valve 82 to the ECU 1.
U1 closes the electromagnetic valve 82 according to the instruction.

In step S202, a work instruction to start the engine is displayed on the display unit 27 of the failure diagnosis device 2, and the repair worker starts the engine.

In step S203, an instruction to maintain the engine speed at, for example, 2,000 revolutions is displayed on the display unit 27 of the failure diagnosis device 2, and the repair worker maintains the engine speed at 2,000 revolutions and fails. When the enter key of the diagnostic device 2 is pressed, in step S204, the failure diagnostic device 2 outputs an instruction to the ECU 1 to forcibly open the electromagnetic valve 82, and the ECU 1 responds to the instruction. The solenoid valve 82 is opened.

In step S205, at the same time when the electromagnetic valve 82 starts to open, the timer starts to start counting the reference clock.

In step S206, an instruction to detect the output signal of the lift sensor 61 is output from the failure diagnosis device 2 to the ECU 1, and the ECU 1
1, the position of the valve body 59 is detected.

In step S207, it is determined whether or not the EGR is open based on the position detection result. When the EGR is opened, the timer is stopped in step S208, and in step S209, the timer is stopped. The count value T1 is stored in the memory.

In step S210, the timer is reset, and further, an instruction is sent from the failure diagnosis device 2 to the ECU 1 to force the solenoid valve 82 to be closed. The ECU 1 closes the electromagnetic valve 82 according to the instruction.

In step S211, the timer starts to start counting the reference clock at the same time as the solenoid valve 82 starts to close.

In step S212, an instruction to detect the output signal of the lift sensor 61 is output from the failure diagnosis device 2 to the ECU 1 again, and the ECU 1 detects the position of the valve body 59 based on the output signal of the lift sensor 61. Is detected.

In step S213, it is determined whether or not the EGR is closed based on the position detection result. When the EGR is closed, the timer is stopped in step S214, and in step S215, the timer is stopped. The count value T2 is stored in the memory.

In step S215, the count value T
1 and T2 are read from the memory and compared with reference values, respectively. If the count values T1 and T2 are smaller than the reference value, it is determined to be "normal". If the count values T1 and T2 are larger than the reference value, it is considered that the response has deteriorated and "EG
R failure ".

FIG . 7 is a flowchart showing a method of diagnosing a failure of the EACV , and FIG. 9 is a diagram showing the contents of diagnosis by the method of diagnosing failure.

When the failure diagnosis is started, step S30
In 1, a work instruction to start the engine is displayed on the display unit 27 of the failure diagnosis device 2, and the repair worker starts the engine.

In step S302, an instruction to detect the temperature of the engine coolant is output from the failure diagnosis device 2 to the ECU 1, and the ECU 1 outputs the detected temperature to the failure diagnosis device 2.

When the failure diagnosis device 2 confirms that the temperature of the cooling water has risen and the engine has sufficiently warmed up, in step S303, the failure diagnosis device 2 controls the electric equipment such as an air conditioner, a power steering, or a headlight which affects the engine speed. The on / off state of the articles is determined, and if these are in the operating state, the fact that they are to be stopped is displayed on the display unit 27 in step S304.

In step S305, it is determined whether or not the throttle valve is in the fully closed state based on the output signal of the throttle sensor (not shown). An instruction to prohibit the operation is displayed on the display unit 27.

When the preparation for the failure diagnosis is completed as described above, in step S306, an instruction to set the valve opening to 10% is first output from the failure diagnosis device 2 to the ECU 1, and the ECU 1 Supplies a current corresponding to the valve opening 10% to the coil 79 of the solenoid 71.

In step S307, an instruction to measure the engine speed is output from the failure diagnosis device 2 to the ECU 1, and the ECU 1 outputs the detected engine speed to the failure diagnosis device 2.

In step S308, the engine speed detected by the ECU 1 is compared with a reference speed previously stored as an engine speed corresponding to a valve opening of 10%. In step S309, the comparison result is obtained. Is displayed on the display unit 27.

In step S310, it is determined whether or not the measurement for all the scheduled valve openings has been completed.
As shown in, the valve opening degree is 30%, 50%,... 100%,
When the failure diagnosis for 70%,..., 10% is completed, the processing is terminated.
Return to 6.

In step S306, each valve opening is sequentially set, and similarly, the consistency between the engine speed and the valve opening is confirmed.

FIG. 8 shows a third embodiment of the present invention.
9 is a flowchart illustrating a failure diagnosis method for the sensor 83.

When the failure diagnosis is started, step S40
In step 1, an instruction to start the engine is displayed on the display unit 27 of the failure diagnosis device 2, and the repair worker starts the engine.

In step S402, an instruction to detect the temperature of the engine cooling water is output from the failure diagnosis device 2 to the ECU 1, and the ECU 1 outputs the detected temperature to the failure diagnosis device 2.

When the failure diagnosis device 2 confirms that the temperature of the cooling water has risen and the engine has sufficiently warmed up, in step S403, an instruction is given to depress the accelerator several times to activate the O2 sensor 83. Is displayed.

When the activation of the O2 sensor 83 is completed, an instruction to remove the connector 17 and bring the test probe 6 into contact with a specific wire harness is displayed in step S404.

In step S405, the repair worker removes the specified connector 17 and sets the wire harness connected to the connector (if the connector connects a plurality of wire harnesses, the specified color 17 The test probe 6 is brought into contact with the wiring harness.

In step S406, an instruction is issued from the failure diagnosis device 2 to the ECU 1 to reduce the fuel supply amount and increase the air-fuel ratio (thin the fuel).
I is controlled to increase the air-fuel ratio.

In step S407, an instruction to increase the fuel supply amount and lower the air-fuel ratio (enrich the fuel) is output from the failure diagnosis device 2 to the ECU 1, and the ECU 1 executes the EF.
When I is controlled to make the fuel rich, in step S408, the timer starts to start counting the reference clock at the same time as the EFI control is started.

In step S409, the failure diagnosis device 2 measures the output voltage of the O2 sensor 83 input from the test probe 6, and when the air-fuel ratio decreases and the output voltage of the O2 sensor 83 exceeds the reference voltage, the process proceeds to step S410. Then, the timer stops counting the reference clock.

In step S411, the count value T3 of the timer is compared with the reference value Tref. If the count value T3 is smaller than the reference value Tref and the responsiveness of the O2 sensor 83 is good, the process proceeds to step S412. Is displayed, the count value T3 is large, and the O2 sensor 8
If the responsiveness of No. 3 is not good, a message indicating "bad" is displayed in step S413.

As described above, the present invention has been described by taking some of the objects to be diagnosed as an example. However, the present invention is not limited to this, and it is difficult to quantitatively determine a fault location and a fault state. What kind of diagnostic object can be used as long as the known state is positively reproduced for the target and a failure judgment is made based on whether the test result obtained at this time is the predicted result or not It is also possible to apply to.

[0090]

As is apparent from the above description, according to the present invention, a known state is positively created by an external signal input, and the inspection result obtained at this time is predicted from the known state. Since the failure diagnosis of each part is performed based on whether the result is obtained or not, it is possible to diagnose a failure in a part where it is difficult to quantitatively determine a failure part and a failure state.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an intake and exhaust system of an engine.

FIG. 2 is a block diagram of an ECU and a failure diagnosis device according to one embodiment of the present invention.

FIG. 3 is a diagram showing output voltage characteristics of an O2 sensor.

FIG. 4 is a diagram showing output voltage characteristics of an O2 sensor.

FIG. 5 is a flowchart illustrating an EGR failure diagnosis method according to the first embodiment of the present invention.

FIG. 6 is a flowchart illustrating an EGR failure diagnosis method according to a second embodiment of the present invention.

FIG. 7 is a diagram illustrating signal contents according to a second embodiment of the present invention.

FIG. 8 is a flowchart illustrating a method for diagnosing a failure of an O2 sensor according to a third embodiment of the present invention.

FIG. 9 is a diagram showing a diagnosis content according to a second embodiment of the present invention.

[Description of Signs] 1 ... ECU, 2 ... Fault diagnosis device, 3 ...
Actuator, 4, 4A sensor, 6 test probe, 10, 20 CPU, 11, 21 ROM, 12,
22 RAM, 15, 25 communication interface, 1
6,17,18 ... connector, 26 ... keyboard, 27 ...
Display unit, 50 EGR, 51 control port, 59 valve body, 61 lift sensor, 70 EACV, 71 solenoid, 73 engine, 74 outlet manifold, 75 inlet manifold, 76 throttle valve, 79 ... Coil, 82 ... Solenoid valve, 83 ... O2 sensor

Claims (3)

(57) [Claims] 1. A vehicle fault diagnosis method for diagnosing a failure of the external signal unresponsive site behavior can not be changed by direct signal input from the outside, the operating condition of the engine
Control to the at the time of setting the external signal unresponsive site surrounding environment to a known state, the externally signal unresponsive quantitatively detect the actual behavior of the site, the quantitatively detected external signal unresponsive A failure diagnosis method for a vehicle, wherein a behavior of a part is compared with a behavior of an external signal unresponsive part predicted from the known state, and a failure diagnosis of the external signal unresponsive part is performed. 2. An external signal non-responsive portion is an O2 sensor for detecting an oxygen concentration in exhaust gas, and outputs a signal for increasing an amount of supplied fuel to lower an air-fuel ratio (air amount / fuel amount) of an air-fuel mixture. 2. The fault for a vehicle according to claim 1, wherein a fault diagnosis is performed by comparing an output value of the O2 sensor detected when input from outside with an output value of the O2 sensor predicted from the known state. Diagnostic method. Wherein the external signal unresponsive site, EG the exhaust gas recirculated to the combustion chamber of the engine through the control valve
An R system, wherein a failure diagnosis is performed by comparing an open / closed state of the control valve when the vehicle is in a scheduled state with an open / closed state of the control valve predicted from the scheduled known state. The vehicle fault diagnosis method according to claim 1.