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A car with a mileage of about 32 thousand km and a F02 740Li powered BMW 740Li car equipped with N54 engines. User response: the car sometimes jumps to neutral while driving, and the engine fault lamp lights up. After the failure light was extinguished, everything returned to normal. Check analysis: the maintenance personnel check the engine control unit, the fault code is: D01557-1 number missing data, receiver chassis control unit ICM, emitter engine control unit DME; D01558-2 torque data loss, receiver ICM, transmitter DME; D0156D - 3 torque data missing, receiver ICM, transmitter DME; D01 No. 570-4 torque data missing, receiver ICM, transmitter DME; D01 B3F - 5 torque data missing, receiver ICM, transmitter DME; D01A08 - 6 torque data missing, receiver ICM, transmitter DME; D01646 - acceleration pedal position data missing, receiver ICM, transmitter DME; missing crankshaft output torque data missing Receiver ICM, transmitter DME; D76F02 - wheel target drive torque data missing, receiver ICM, transmitter DME. Analyzing the contents of fault codes, we find that their common feature is data missing. Clear the fault code after the road test. When the vehicle passes through the deceleration zone, the fault lamp suddenly lights up, then the engine appears idling. After checking the engine control unit after emergency stop, it is found that the fault code is exactly the same as the original one. Analyzing the characteristics of fault codes, we can see that the data involved are not directly obtained from sensors, but calculated. This shows that the problem lies in the data transmission between control units. For vehicles with stable control function, the driving torque of each wheel is individually controlled. If the chassis control unit does not get the correct torque data, it may affect the direction of the vehicle. So in this case, the chassis control unit will cut off the power transmission of the engine. This is the reason why the engine is turning. The communication status of ICM and DME in power system LAN is normal through gateway control unit. As the fault is accidental, it is necessary to speculate on the fault point according to the nature of the fault code. The vehicle fault is limited to the 2 control units of ICM and DME, and does not involve data bus of local area network. Then we have to decide which of the 2 control units is wrong. From the content of the above fault code, we can see that the engine control unit is aware of all the data items and destinations to be sent. It also indicates that the engine control unit is also aware of the fact that the data is not delivered. The chassis control unit is re detected and no fault codes are found. This indicates that the engine failure unit should be the engine control unit. Troubleshooting: replace the engine control unit and encode it. Repeated road test to determine the fault completely eliminated.