Method of using car electronic control engine self-diagnosis system
First, the working principle of the self-diagnosis system
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When the vehicle engine electronic control system is working, the self-diagnosis system detects the abnormal input and output signals as fault signals.
There are mainly the following types of self-diagnosis system failures.
1. When a signal of a certain circuit exceeds the specified range, the fault diagnosis system determines that the circuit signal is faulty.
If the water temperature sensor is normal, its output voltage signal will vary from 0.1 to 4.8V. If the cooling water temperature sensor output voltage is lower than 0.1V (corresponding to water temperature higher than 139 °C) or higher than 4.8V (corresponding to water temperature lower than -50 °C), the ECU determines that it is a fault signal and stores it in the memory.
2. When the engine is running, when the ECU does not receive the input signal or input signal of a certain sensor for a period of time, the ECU also determines that it is a fault signal.
When the engine is operating at the normal operating temperature, the ECU does not detect the output signal of the oxygen sensor or the oxygen sensor signal for more than one minute between 0.3 and 0.6 V for more than one minute, that is, the oxygen sensor circuit is faulty.
3. In the normal operation of the engine, if an abnormal signal occurs by chance, the ECU diagnosis system will not judge as a fault. Only when the abnormal signal continues for a certain time or multiple times, the ECU will judge it as a fault. If the engine speed is 1000r/min, the speed signal (Ne signal) will lose 3-4 pulse signals, and the ECU will not judge The Ne signal is faulty. At the same time, the "CHECK" lamp will not light, and the fault of the Ne signal will not be stored in the ECU.
It should be noted that the fault determined by the ECU can only provide the nature and scope of the fault. For example, when the wiring between the water temperature sensor and the ECU is broken, the water temperature sensor output voltage signal will be higher than 4.8V (normally 0.l -4.8) V). At this time, the fault information determined and output by the ECU is that the water temperature sensor has failed. The final determination is the failure of the sensor, actuator or corresponding wiring, and should be further checked and determined.
Second, the way to display fault information
After the ECU fault self-diagnosis system detects that the fault signal is determined to be a fault, the fault information is stored in the ECU memory in the form of a fault code. The fault code or fault data is displayed in a specific way through a certain operating procedure. Different types of vehicle fault information are displayed in different ways. There are mainly the following types:
1. The fault code is flashed by the CHECK (check engine) light.
When the engine is working normally and there is no fault, turn the ignition switch to the "ON" position and the "CHECK" lamp lights. This lamp should be extinguished when the engine speed is higher than 500r/min after starting. Otherwise, if there is a fault, use a special jumper to bridge the diagnostic seat or use other operations to display the fault code in a certain flashing manner of the “CHECK†light. After troubleshooting, the “CHECK†lamp is extinguished when the engine speed is above 500r/min.
2. Use the LED (fault display) lamp to bridge the fault diagnosis output terminal on the diagnostic socket, or connect the special detection instrument, such as the percentage meter, the angle bracket, the computer detector, etc. to directly read the fault code or fault information.
3. The fault code is displayed by the side of the main computer ECU housing.
4. The fault code, information data and data are directly displayed by the display on the instrument panel.
Third, the removal of fault information
After the fault is removed, the fault information is still stored in the ECU and cannot be automatically cleared with the fault. It must be passed through the operating procedure. The cleaning method for different models is also slightly different. The general cleaning method is to unplug the “EFI†fuse in the fuse box for more than a few seconds, but there are exceptions.
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