A mileage car with a mileage of about 30 thousand km, carrying a CLS engine and a 09G automatic transmission in 2013. User response: all doors and windows of the car can not work. Inspection and analysis: the maintenance personnel test the car, found whether to operate the driver's side elevator switch, or the individual operation of the door elevator switch, the 4 doors of glass elevator do not work. Using diagnostic VAS6150, it is found that the fault code is stored in 09 central electrical control unit: 03020 - local data line 2 circuit failure. The data flow of the elevator switch is read, and it is found that the control unit does not respond to the operation of the switch when pressing the elevator switch. The Bora vehicle adopts BCM integrated control of vehicle body control unit (integrated J519, J533 and J393). All kinds of single relays and actuators are highly integrated, which greatly reduces the failure rate and increases the comfort of vehicles. The comfort system adopts the single line control of LIN bus. When the glass elevator is operated, the elevator switch signal is transferred to the door control unit, and the door control unit transfers the signal through the LIN bus to the central electronic device control unit J519. The J519 passes the analysis data to make the judgment of the rise and drop signals, and then passes the LIN bus to the control units of the door and the door control of each car. The unit controls the work of the elevator. According to the working principle, fault code and data flow analysis, the fault is locked in the LIN bus, vehicle body control unit and door control unit. The LIN bus is tested according to the circuit diagram to see whether there is short or open circuit in the LIN bus. Turn off the ignition switch and disconnect the negative line of the battery. The T73a connector of BCM is removed to measure the resistance between bus T73a/17 and grounding iron, which is 26.4 ohms. The connectors T10I, T6i, T6j and T6k are disconnected respectively, and the resistance between T73a/17 and the grounding iron is measured. When the T6k is open, it becomes open and normal. The fault is locked in the right rear door control unit J389. Troubleshooting: replace the right rear door control unit, troubleshooting.