Symptom:
    A 2007 production of the popular Passat 1.8T led Yu automatic car, equipped with BGC engine and 01V hand 5-speed transmission, mileage 2025km. The owner of the rescue call reflects the car in the face of a red light when the engine suddenly turn off the engine, many times can not start the car. Rescue personnel rushed to the scene for preliminary inspection, in the ignition switch ON state, the instrument board in addition to EPC lights and brake pedal light is not bright, the other information shows no exception. Try to start the engine, the engine can start, but after running for about 1s, then go out. Try to start again, the fault remains the same, the overall feeling and the phenomenon of anti-theft lock similar to the engine, but the anti-theft indicator K117 is not lit or flashing, so the car into the repair station for further inspection.
    Failure analysis:
    Connect the VAS5052 fault diagnosis instrument, enter the engine control unit J220 query fault memory, the screen display to identify a fault code: 18056 - drive system data bus failure. And the fault code can not be cleared, is a non-incidental failure. Select the data block function option, read the engine control unit and the power system data bus other control unit communication between the measured value, 125 display group: transmission 0, combination meter 0; 126 show group: airbag 0, that J220 and transmission And the airbag control unit communication is completely interrupted.
    The device on the CAN data bus has the engine control unit J220, the automatic transmission control unit J217, the combination instrument control unit J285, the ABS control unit J104 and the airbag control unit J234. It is necessary to use the VAS5052 Fault diagnosis instrument into the gateway control unit J533, with the perspective of the gateway to check the entire power system CAN data bus communication status to determine the data bus engine control unit can not communicate the nature of the failure to determine the cause of the fault is the data bus interference, Or the data bus link is short-circuited or partially disconnected.
    Into the instrument integrated control unit J533 query fault code: 01314 - engine control unit no communication, the current existence; 01315 - transmission control unit no communication, occasional. Execute the operation to clear the fault code, 01314 can not be deleted. Select the data block function option, read 125 display group of measured values: engine 0, transmission 1; 126 group of measured values: airbag 1. The above inspection shows that the gateway and the power system in addition to the engine other than the control unit communication is normal, the fault nature of the engine control unit and the power system data bus between the local circuit.
   From the engine can start running 1s analysis of the phenomenon, the engine control unit power supply should be no problem, VAS5052 can access the engine control unit can also prove that the power supply is normal, thus judging the engine control unit J220 can not communicate for two reasons: First, the engine control unit And the data bus connected to the external line interrupt, the second is the engine control unit J220 CAN data bus transceiver part of the damage occurred in the circuit. According to the above analysis we can see that the next step as long as the power system CAN data bus to check the status of the external line can determine the cause of the malfunction.
    Check the BGC engine circuit diagram, find the engine control unit harness side connector T121 / 58, T121 / 60, and the combination of instrument control unit harness side connector in the T32b / 20, T32b / 19, respectively, for the power system data bus CAN-L (orange / brown) and CAN-H (orange / black) connection terminals. Disconnect the connector of the engine control unit and the green connector of the instrument control unit to measure the continuity of the corresponding terminal of the J220 connector harness side and the J285 connector harness side. The measurement results show that the resistance between the T201 / 58 terminal of J220 and the T32b / 20 terminal of J285 is 0.2Ω, the resistance between J220 T121 / 60 terminal and J325 T32b / 19 terminal is 0.5Ω, which means that J220 and J285 The external data bus link is not open. According to the above checks concluded that since the data bus external line is normal, the cause of the failure can be determined as the engine control unit within the data bus transceiver is a problem.
    Troubleshooting:
    Replace the new engine control unit and place the ignition switch ON. The EPC lamp and the brake pedal indicator light on the meter. Connect the VAS5052 to the gateway J533 again, and check the data of the display block. The display value of the display group is shown as: Engine 1, Transmission 1. This indicates that the engine control unit communicates with the data bus back to normal. Clear the control unit stored in the fault code, with a password reader to read the car's 4-bit anti-theft password, enter the boot function options to complete the J220 encoding and J220 and J285 between the anti-theft match, the throttle control unit J338 Make basic settings. Complete this series of operations, start the engine, the engine started a smooth start, road test to confirm the engine in the normal conditions of work, complete troubleshooting.