a 2009 annual Shanghai Volkswagen Skoda Octavia 1.6 L car, mileage of 21,000 km, the user reflect each car dashboard lights were lit suddenly during driving, the engine tachometer, speedometer hands swing back and forth, the multifunction display also displays fuel vehicle traveling 10 km, but the pointer at this time indicates a normal fuel gauge. After re-starting the vehicle, general instrument to return to normal, but the multi-function display shows for a while to return to normal. In addition, it says users, the fault in the car used by more than one-year period is already the third time there, the first two times, respectively, appeared in 2009 October and November. In addition, the failure of the car has been revised several times in the other service stations, and has replaced the on-board network control unit (Fig. 1), but the fault has not been able to be resolved.
FIG 1
After receiving the vehicle, connected to the author of the vehicle fault diagnostic testing and found that many of the control unit are stored on each of the network control unit communication error fault code, it appears that the car is likely related to the failure to communicate with the network. To troubleshoot network communication system of the car, the car must understand the network communication system. The car using the system bus and driving comfort system bus (FIG. 2), the bus drive system includes an engine control unit, automatic transmission control unit, ABS control unit, the airbag control unit, an electric power steering control unit or the like. The system bus is comfortable and the steering column includes an electronic control unit, automatic air conditioning control unit onboard power supply control unit, control unit and other comfort systems. High-speed network bus driver comfort system bus to a low speed network, the communication between the two networks is achieved through the gateway J533.
FIG. 2
For this sporadic fault exclusion, is preferably able to trigger a fault occurs, so that you can capture some important clues fault. In order to be able to get some useful information, the author ED user asked in detail about some of the specific conditions of failure symptoms. By exchange with the user, the author summed up the initial failure of the laws of the car, ie failure after each occurrence are open heater. Then open the warm air test failure will not occur in a timely manner it? Several attempts by the author, the fault has not reproduced. In view of the carNow the main fault are reflected on the meter, I suspect there may be a problem with the instrument cluster itself. To rule out the possibility of instrument failure, I decided to replace the instrument (Figure 3), allowing users to continue to use, to see whether there will be a failure.
3
After several days of use, said the failure to call the user again. Depot the vehicle, connected to the author of the vehicle fault diagnostic detection, the control unit are stored in each of the meaning of the other control units of the network error code transmission error. Based on our experience in the maintenance, fault for the CAN bus system, and more generally node failure and related communications line failure. If a control unit is out of the question, other general fault codes stored in the control unit will be directed to the control unit. Therefore, the car is likely a fault on the line. After
, I decided to check the relevant communication lines. But in the process test again to try to trigger a fault, when an emergency brake failure appeared. Then once again hard braking the vehicle and found that failure will occur. Since it is a failure occur during emergency braking, further evidence that the problem lies on the line. Is it a problem in the vicinity of the instrument panel line? At this point vehicle diagnostic connection failure is detected, the device control unit drives a display system are not reach, and the electric fan at high speed. Later I also found extruding dashboard malfunction occurs, it seems the problem lies in the vicinity of the instrument panel line. I remove the plaque meter section of the audience, through careful observation, finally found a break point harness (Figure 4) is squeezed deformation. It was determined that the cause of the malfunction is car driving the bus is shorted to ground line high.
Figure 4
After the repair broken lines, test troubleshooting.
Summary: For fault car, I believe that: the drive upper bus line is shorted to ground, the bus signal transmission exception causes the drive to a plurality of warning light is lighted. Due to the vehicle speed signal system from the ABS wheel speed signals, when the system is out of ABS wheel speed signal, to affect the control unit calculates the correlation of the vehicle mileage. Perhaps the system in order to avoid false information to mislead the driver, the system displays the vehicle mileage of only 10km, to remind users to repair vehicles. Later we encountered in the maintenance of a situation comfortable bus shorted, there will be the same failure symptoms and drive the bus high line-to-ground short circuit. The reason why open heater will fail, because the dashboard side after the heat deformation easily squeezed.
(Di Yuanwu)