BCM has a mileage of about 62 thousand km, with a displacement of 1. 3L and a five speed transmission of Nanjing Fiat car. When the vehicle is running normally, the engine suddenly stalls, and the engine can not start again after the engine is turned off. When a fault occurs, a yellow "CODE" indicator will appear on the instrument cluster, and the coolant temperature indicator lights up, and the coolant thermometer pointer returns. Position, when the ignition switch goes to "MAR" position, the oil indicator light does not shine. When the battery negative cable is removed from the 10min, it will be installed again, and the car will return to normal. But after a certain period of time, the fault will be reproduced. Fault diagnosis: when the fault occurs, the fault detection instrument can not enter the relevant program, the car work is restored to normal by the method of power failure, and the fault detector is used to enter the body control unit (). The fault content is closed by the CAN bus. When entering the combined instrument, the fault content is CAN bus shutdown and intermittent fault. The above fault code can be cleared. But when the engine breaks out again, the trouble codes will be reproduced. When checking the ignition system of the car, it was found that the spark plug was replaced by a small impedance spark plug in the external repair plant, and the original car was used as a high impedance spark plug in the European system. The resistance value at the two ends of the spark plug on the car is measured by multimeter, which is 4~5 ohms. The resistance of the spark plug used by the car is 4.7 ~ 4. 8K ohm. It is considered that the failure is caused by the analysis. Replace the original spark plug, remove the battery negative cable and reinstall it. The ignition switch is transferred to the "MAR" position 10s and then to the "STOP" position 30s, so that the engine electronic control system is self-learning and the fault detection instrument is used to clear the memory of the control unit. After commissioning, everything is normal, and the trouble is completely eliminated.