The mileage is about 120 thousand km, the 2008 Volkswagen Langyi 2 automatic car equipped with CEN engine and 09G manual transmission. User response: the driver's side window button does not control the front passenger side windows. Inspection and analysis: inspection by maintenance personnel found that the door window can be properly controlled by using the front window button on passenger side door. Use the VAS6150 fault diagnosis instrument to inquire the memory of the body control unit J519 failure, report the fault code 01331, the driver side door control unit J386 loses communication. Read the relative measurement value, 12 groups of 1 zone driver side window switch E40, 3 front row passenger side window switch E81 lifting signal always show not operated, and the reported fault code. There are 3 reasons that affect the communication between control units, that is, power supply, communication line and control unit. The communication between J386 and J519 depends on the LIN bus. From the fact that the driver's side door car window is normal, the J386 power supply has no problem, and the remaining problems can be determined by checking the communication line. Check the LIN bus between J519 and J386. The LIN bus between the two buses has a T10a connector on the left A column. Disassemble the driver side door trim panel, disconnect the J386 connector, use the LED test lamp to access the T10f/3 terminal test, and do not light up. The 9.15 V voltage can be measured on the side of the T10a/10 terminal near the wiring harness of the car door. It can be seen that the LIN bus breakpoint is located in the driver side door wiring harness. Troubleshooting: repair line, troubleshooting.