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A mileage car with a mileage of about 90 thousand km and a ZRE120L corolla car equipped with a 1ZR engine in 2011. User response: when the vehicle is running, it will automatically extinguish without any precursors. Fault diagnosis instrument IT2 detection, no fault code. No problem was found in the data flow. The fuel pressure was measured at 300 kPa with an oil pressure gauge. Equipped with an oil pressure gauge, it was found that when the fault occurred, the oil pressure could be maintained at 300 kPa, so the oil pressure problem was eliminated. Check the connector of the engine control unit, no loosening and corrosion. The wiring harness of the engine control unit harness and the body control unit is rocking, and the failure can not be reproduced. The active timing test of the variable timing system VVTi is carried out by IT2, and the engine stall is tested, which indicates that the system is normal. Using the same type of vehicle engine control unit to do the swap test, the fault is still. At this point, the maintenance personnel feel helpless. Inadvertently in idle speed, the original light to turn, 2 consecutive flameout. So remove the meter, check the ignition switch, no abnormalities. In the light of the direction, the fault is not reproduced. Many tests have no fruit, so it has to be returned to the instrument. However, when the instrument is pulling the wiring harness, the fault is reproduced. Repeatedly pulling the wiring harness, the fault becomes controllable again. Finally, it is found that sometimes the fault is reproduced frequently when the wiring harness of the body control unit is patted. The car body is replaced by the body control unit of the accident car. After several long time tests, the fault has not been reproduced. The body control unit of the original car is reproduced. The interior of the body control unit is only a multi pin connector, which should not be so easily damaged. So the body control unit connector was re examined. It was found that there were signs of loosening of the 2 pin connector of the B2 connector from the main line of the engine. Inspection and analysis: the maintenance personnel together with the user test run, after about 30 min failure occurs. Then no matter how to try, the failure no longer appeared. Consult the maintenance record. The car is in good condition and no accident occurs. Dismantle the installed anti-theft device and restore the original line. Continue the test, when the idle speed of another failure. Troubleshooting immediately: repair the connector, repeat the trial run, and the fault does not appear. After several visits, the failure has not been reproduced and the fault has been completely solved.