Symptom: Volkswagen Passat B51.8T sedan, because the central control lock and electric glass lifter can not work to station maintenance.
    Troubleshooting: After repairing the car, the maintenance staff to carry out a preliminary inspection of the car and found that the ignition switch regardless of opening and closing, only the left front door of the central locking and left front door of the electric glass lifter can work properly, other windows of the electric The glass lifter does not work; but if you press the other windows and doors to control the window switch, all doors and windows switch can work properly. When the door is closed, the car key is inserted into the keyhole of the left front door, unlocked and locked, and only the left front door door lock can be opened and closed; if the key is kept in the unlocked or locked position, only the front door of the electric glass Lifter can work up and down.
    After the actual operation of the above check, the initial identification of the car's comfort system there is a certain fault. Then, with the VAS5052 vehicle diagnostic equipment to check the comfort system, connect the instrument and open the ignition switch, enter the comfort system central control module (46) query failure, the instrument screen display query to the following seven faults: ① with the left front door and window module no communication. ② There is no communication with the right front door and window module. ③ No communication with left rear door and window module. ④ There is no communication with the right rear door and window module. ⑤ No communication with CAN data bus diagnostic interface J533. ⑥ Comfort system data bus single line operation mode. ⑦ The control module is incorrectly encoded.
    In order to view the comfort system code value, re-enter the comfort system unit module, look at the module version information, found that the code is 00017, is indeed incorrect. Then use the VAS5052 to correctly encode the 00259 of the comfort system and clear all fault records. The incorrect recording of the control unit and the fault record of the CAN data bus single line operation mode have been cleared, but the other faults still can not be cleared. It seems that these can not clear the failure may be caused by the car electric glass lifts and central locking can not work the main reason. Because the signal between the four-door control module and the central comfort system control module of the Passat B5 sedan is transmitted via the CAN data bus, the CAN is the abbreviation of the controller's local area network. The comfort system CAN data bus is connected by two mutually twisted signal lines The same data is passed, one for CAN-H (orange / green) and one for CAN-L (orange / yellow). All the control modules of the comfort system are connected to two lines for data exchange and signal transmission. In addition, the data bus diagnostic interface located in the combination meter is also kept in communication with the data bus to detect the working status of the bus. In order to pass the signal correctly and effectively, the two threads are twisted together like twist, and the pulse signals transmitted on the two lines are the same, but the opposite is the opposite. If the door control module and the comfort of the central control module between the CAN can not communicate properly, it will lead to the left front door module to the control switch signal can not be properly transmitted to the other three door control module, and all the door control module can only receive Directly input to the module of the electric glass lifter switch signal. Therefore, the key to troubleshooting the car is to find the door control module and the central control module CAN can not communicate the reasons.
    In order to determine the central control module, the door control module and the data bus connection, through the VAS5052 into 46-08-012, observe the data set measurement, 4 sets of data with "1" or "0" values ​​represent the driver door, Right front door, left rear door and right rear door module and the comfort system central control module CAN data bus connection status, this time 4 sets of data are "0", indicating that the door control module and bus communication is indeed faulty, but still can not Determine the specific point of failure.
   In order to further find the root cause of CAN can not communicate, the maintenance personnel first disassemble the comfort system central control module (located in the driver's side seat floor) to check, in the demolition of the module, found that the car is already repair the accident car, floor comfort system And the left A column of the comfort system of the harness has been seriously damaged and has been repaired. Maintenance personnel on the wiring harness to conduct a specific inspection, focusing on no twisted CAN bus finishing.