A Volkswagen Sagitar car with a mileage of about 130 thousand km in 2009. User response: the vehicle airbag warning light has been repeatedly reported to the police without any regularity. Inspection and analysis: the maintenance personnel detected the airbag control unit and found the fault code 01317 - there was no communication with the instrument control unit. Detection instrument control unit, and found multiple incidental fault codes: 01290 - data bus J533 interface without communication; 01299 - data bus J533 unreliable signal; 01309 - no communication; 01314 - no communication of engine; 01316 anti lock braking system no communication; 01321 - Airbag no communication. It is also found that there are many failure codes in the gateway control unit which can not communicate with the control unit such as engine and ABS. Combined with the above fault hints, it is judged that there is bus failure in the LAN of power system. Moreover, bus failures occur at different network areas, indicating that failures are related to gateway control units. Troubleshooting: replacing gateway control unit and troubleshooting.