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A Audi A8L car with a distance of about 12 thousand km. Customer reflection: the steering wheel deflection, ESP system alarm, air suspension alarm, dynamic steering system alarm, four wheel drive system alarm, ACC system can not be used. The control units involved in these systems have fault codes, and the occasional "received error values lead to function constraints", "functional closure", "unreliable signals cause functional damage", and the upper limit of "the effect of overload on function". Update the steering column of the dynamic steering system according to the fault navigation test plan, but the fault remains unchanged. Further inspection revealed that the steering column control unit J527 could not communicate, and there was no J527 in the gateway installation list. According to the analysis of the network structure and circuit diagram of the vehicle, the control units involved are all control units on the FIexRay bus. They disconnect each control unit to observe the changes, disconnect the gateway J533 and try to be invalid. The suspension control unit J197 is disconnected according to the difficulty of the installation position. The power line that has an external connection beside the J197 is found before disconnection. It is found in the power line. It is found that the car has an unknown control unit in the gateway J533 wire bundle. It is suspected that the control unit interferes with the signals on the FIexRay bus and disconnects the unknown control unit. It is found that the J527 communication is normal and all the faults are eliminated. The user knows that the car does not have the function of reversing image when the car is out of the factory. The user is convenient to use the reverse vehicle camera system of non original car for the convenience of use. The use effect is exactly the same as the original car system, which interferes the maintenance personnel's judgment of the fault. The unknown control unit is the reverse vehicle camera control unit of the non original car configuration.