Symptom: a 2009 annual production FAW - Volkswagen New Bora car, mileage of 3784km, equipped with BWH 1.6L engine. According to the user to reflect the start of the car when the starter will start the normal work but not the phenomenon of the car, but wait for a while and then start a normal car.
    Check the analysis: access to the car's maintenance records and found that failure can not start has occurred three times. The first time a failure, the user calls for rescue, maintenance personnel to the scene after the start of the car can be successfully tested repeatedly. Use the fault diagnosis device to detect, store the "key identification error" temporary fault code, maintenance personnel to clear the trouble code so that users continue to use observation. A few days later, the user came to the phone to reflect the vehicle can not start, maintenance personnel arrived at the scene and can be a smooth start a car. Use the fault tester to bring up the same "key identification error" of the same time the temporary fault code, maintenance personnel suspected key problems, allowing users to use another key to continue to observe. The rescue has only passed a few hours, the user again to call the car can not start the car, the failure of many times to make users complain very much.
    Maintenance personnel arrived at the scene, did try out the occasional start of the vehicle can not be the phenomenon of the car, and the two keys are occasional start the car situation. Check the vehicle for any other symptoms, found that the failure of the power windows and skylights can not be opened, if the power windows and skylights can be used normally, the vehicle can also start the car. So what is the relationship between the two fault phenomena?
    The new Bora sedan uses Volkswagen's fourth generation anti-theft system, the security and stability is better, the body control unit BCM combines the power management control unit J519 and the comfort system control unit (gateway) function. Combined with the car stored "key identification error" fault code and power windows and skylights can not open the fault phenomenon, I believe that the anti-theft system and body control system should be checked. First use the fault diagnosis instrument VAS5052 into the body control unit BCM, read the data stream, found that BCM can identify the windows and skylights open and close the state, indicating that the windows and sunroof switch and BCM line between the normal. According to the window control circuit diagram analysis, the window control process is as follows: window lift switch → door control unit → LIN bus → BCM, and then issued by the BCM windows of the opening signal → door control unit → window motor. In the above check, you can see that BCM can receive signals from windows and sunroof switches using a diagnostic tool. All windows should not work. BCM does not have a work order (because all door control units are not likely to fail at the same time Very small). Will BCM work poorly? If BCM is not working properly, it will not only cause the window and skylight to be opened, but also because the BCM has the function of the gateway, it may cause the anti-theft system control unit to communicate with the engine control unit badly, causing the inability to start. Based on these analyzes, the author removed the BCM and its power supply and ground line to measure.