Fault phenomenon
    A 2004 Passat B51.8T, mileage 10000km. The car due to traffic accidents into the repair shop repair, maintenance work after the completion of all normal. But shortly after the delivery of the engine can not start the normal phenomenon (in the engine after 2s automatically turn off), then into the factory maintenance.
    Troubleshooting
    To the factory maintenance engine can start, indicating that the car's ignition system and fuel systems are no problem. This phenomenon is like a security system is enabled, but the anti-theft alarm light is always not lit, can not re-match the anti-theft system. In the "code priority" principle, first check the fault code from the start. Through the special diagnostic apparatus, in the engine control unit to read two fault codes, respectively, 18056 - power system data bus communication failure and 17978 - the engine control unit is anti-theft control unit latch. In the central instrument control unit and the gateway controller also has a fault code 01312, indicating that the power system data bus is faulty.
    As the engine does not work properly, of course, can not analyze the dynamic data flow and help find other reasons. So start with the display of these points of failure to rule out. Passat B51.8T car is the use of CAN-BUS bus and multi-channel information transmission system control of the vehicle, the vehicle has two sets of bus network system - a set of power system bus, a comfortable system bus. Power system bus connection Engine control unit, instrument control unit, ABS control unit, airbag control unit and automatic transmission control unit, using star connection. Through the analysis of the two fault codes, the reason for the failure is that the power system data bus is likely to be faulty or defective (ie, poor data communication quality). And the car's anti-theft controller installed in the instrument assembly, if the instrument control unit and the engine electronic control unit due to link disruption and can not communicate, it will happen "engine control unit is anti-theft control unit lock" failure. Therefore, it is important to check the network communication link of the instrument control unit to the engine control unit.
    Troubleshooting
    Remove the instrument assembly shell, along the connection harness down to find and found in the engine compartment and driving the connection to the firewall line hole at the network line wear and wear and tear. Wrap the abrasive skin with tape and fix it with a rubber ring, remove the fault code, troubleshoot, and start the engine normally.
    Maintenance summary
    After the analysis, the reason for this failure is that the cable is not fixed firmly. In the repeated pull and wear in the insulation layer is destroyed, resulting in grounding, which led to the instrument control unit and the engine electronic control unit due to link disruption and can not communicate, so there is a similar anti-theft system to start the phenomenon.
    With the rapid development of modern automobile industry and electronic technology, more and more electronic devices on the car. In order to achieve data sharing and cabling convenience, CAN-BUS bus and multi-channel information transmission system is more and more widely applied to the car, and have replaced the traditional way of wiring trends. This requires us to constantly update the traditional concept, that the car is no longer a few big assembly, and become a variety of devices linked to the whole. In the maintenance of the car, we must pay attention to their relationship, pay attention to "pull the whole body" the possibility.