Passed many trials. I found the rule of occurrence of the above-mentioned failure: only when the car is running continuously, the automatic transmission will lock the gear and enter the protection mode. At this time, if the engine is turned off for a few seconds and the car is driven again, the automatic transmission will resume normal operation. According to the analysis of the failure law, the temperature of the engine and the automatic transmission changes significantly with the driving time, which is likely to be a stable display of a certain control or working element of the automatic transmission. Check the intake manifold, there is no air leakage; check the throttle control mechanism, there is no problem; check the idle motor, it is normal. Then read the dynamic data stream of the engine and found that 4 items of data are abnormal. The 4 items of data are: the fuel injection pulse width at idling speed is 7.30ms (the normal value is 2.6ms), and the signal voltage of the intake manifold absolute pressure sensor is 3.3V (the normal value should be 1.sv), the number of steps of the idle motor is 102 (the normal value is 30), the ignition advance angle is l-20, and it is unstable. Comprehensive analysis of the above four data, the focus of the contradiction is concentrated on the intake manifold absolute pressure sensor, its signal voltage is too high, making the injection pulse width increase. At this time, the oxygen sensor detects that the mixture is too rich.
The engine electronic control unit then instructs the idling stepper motor to increase the air intake, which results in an increase in the number of idling steps, and the engine electronic control unit also constantly adjusts the mixture. The inspection shows that the intake manifold is not leaking. Further inspection found that the engine accelerates vigorously and has good power. It shows that there will be no problems with the wrong valve phase and the clogging of the exhaust pipe. Apply vacuum to the absolute pressure sensor of the intake manifold through a vacuum gun. The sensor indicates that the sensor is normal. According to the inspection results of the above steps, it is concluded that the fault location may be in the EGR system. After disassembly and inspection, it was found that the EGR solenoid valve was stuck in the open position, the exhaust back pressure pipe was broken, and the exhaust back pressure valve base was severely cracked. Troubleshooting after replacing the EGR solenoid valve. Based on past experience, the first thing that comes to mind is the automatic transmission control unit. It is suspected that some of the electronic components will function abnormally at high temperatures, so I replaced it with an automatic transmission control unit of the same model that was running normally and tested it. The failure still failed. exclude.
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