A FAW Volkswagen ten miles car with a mileage of about 80 thousand km. The car lights up with airbag lights during the driving. Fault check: the air bag control unit is detected with the engine detector to store the fault code 01221 (the driver side side airbag collision sensor) and 01222 (the side side side airbag collision sensor on the side driver side); the fault code is cleared by the engine detector, and the fault code is cleared only at first, and the battery is disconnected. After the line is reconnected, the fault code 01222 is cleared. Road test, a straight line running 3-4 kilometers, the airbag lamp on the meter is lit again, and the fault memory stores the fault code again. The collision sensor is directly connected to the control unit; the failure is not ruled out; the replacement of the airbag control unit, the failure continues, indicating that the fault is in the collision sensor. Troubleshooting: replace side driver side airbag collision sensor, road test, troubleshooting. Fault analysis: the failure of the wiring harness and control unit can be eliminated according to the preliminary analysis of the circuit diagram; the relationship between the driver side side airbag collision sensor and the side side airbag collision sensor on the side side of the driver's side is mutual detection. In other words, if there is a right collision, the driver side side airbag collision sensor, the side side side side airbag collision sensor and the right to left collision signal are obtained simultaneously; if only one collision sensor has a collision signal, the other side has no signal, such as the side side side side airbag collision sensing. The collision is detected by the device, but the collision signal is not detected on the left side. The air bag control unit can not judge which sensor has a fault, so it can only be reported at the same time, that is, the air bag light is lit, and it should be understood as "signal unreliable".