The mileage is about 90 thousand km, the 011 year Volkswagen Langyi 1.6 car equipped with CPS engine and 09G manual transmission. Users reflect: the front door of passenger car side door electric window can not be controlled by the driver. Inspection and analysis: the maintenance personnel test car found that the front row of the bus switch E107 can be operated normally, which indicates that the front passenger side door control unit J387 is still able to work. However, with the passing of inspection time, all doors and windows were unable to work. At this time, it was found that the button lights on the 2 rear door electric window switches were not lighted. The power supply of the rear door electric window control unit is controlled by the relay in the switch panel of the driver's side electric window, while the relay is controlled by the driver side J386 (Fig. 1). Check the output voltage of the T8a/3 terminal (yellow / blue line) of the switch board connector, and the 12V test lamp does not light up, indicating that the S37 power supply is abnormal. Measure switch board T16c connector T16c/14 terminal (green line), test lamp is not lighted, indicating that J386 does not output control signal to relay coil. Disconnect the connector on the J386 and reconnect it to power down. At this time, the power of the rear door electric window control unit has been restored to normal, but the window of the front passenger side door can not be controlled by the control switch E81 on the driver side. Connect the VAS5052 fault diagnosis instrument to query the body control unit J519 fault memory, identify 2 static fault memory, 01332 - passenger side door control unit J387 no communication; 03020 - local data bus 2 circuit fault. The car has no rain and light sensors. The circuit diagram of Langyi car shows that there are only 1 LIN buses for J519, and 2 of the local data bus refers to the daily N bus of the front passenger side electric window control unit. Click on the measurement function option to read the signal input of the 12 groups of drivers' side door electric window switch E40 in the 1 area. When the switch E40 is operated, although the window motor works, the measurement value always shows that it is not operated. This case shows that although the J386 has received the E40 request signal and also executes the lifting instructions of the electric window, the J519 does not get the status data of the E40 switch. The same is true for the measurements of the front row passenger side electric window E81 in the 4 group of 3 districts. In view of this, LIN bus data exchange is not carried out between J386 and J519, and the 03020 fault code is true. Remove the door trim panel on the front passenger side and disconnect the J387 T6d connector. Read 12 sets of measurements again. When the operation switch E40 and E81, the measurement value is displayed as operation. Using multimeter to measure the LIN bus voltage on J386, it is found that the J387 connection is 1.025 V and the 8.650 bus is off. This indicates that the voltage of the LIN bus is pulled down because of J387, which is intuitively clear that the LIN data bus transceiver in J387 has a fault, so the bus does not work after J387 is connected and the J519 can not get the state data of the electric window switch. Troubleshooting: replace front passenger side door control unit and troubleshooting. Add-on: Langyi car remote control lock door, one key window lifting condition is that all electric windows are automatically set up and down. If the door control unit is replaced and the key is kept in the lock core hole of the door for a long time and the window can not be automatically lifted, the remote control can not achieve a single key window. At this time, the location of the top and bottom stops of the electric window should be studied. Some cars need to learn many times to complete.