In 2007, Volkswagen Passat controls the 1.8T automatic car with a mileage of about 120 thousand km, equipped with BGC engine and 01V automatic transmission. User response: when the vehicle is running, it releases the accelerator pedal and sometimes flameout. Inspection and analysis: maintenance personnel detect engine control unit and find it impossible to enter. Detection of other control units, the same situation. Measuring the data bus voltage of the engine control unit is normal, indicating that the bus is still working. The diagnostic socket of the vehicle should be connected with the LAN through the gateway control unit. In the case of normal network bus work, the fault diagnosis instrument can not access all control units in the network, which is probably the failure of the gateway control unit. The vehicle gateway control unit is run by the instrument control unit. After replacing the instrument control unit, the fault diagnosis device can access all the control units normally. Detect engine control unit and find fault indication of mixed gas too thin. Observation data show that the data given by the air flow meter are obviously inconsistent with the actual intake volume, which is the direct cause of the over dilution of the mixture. Troubleshooting: replace air flow meter, test run confirm troubleshooting.