A Shanghai Volkswagen Passat 1.8T automatic passenger car with a mileage of over 230 thousand km and a AWL engine equipped in 2004. User response: the anti lock braking system (ABS) alarm lamp lights up. Inspection and analysis: the maintenance personnel detected the ABS control unit and found that there was a hint of the intermittent fault of the left front wheel speed sensor G47. The resistance of the left front wheel speed sensor G47 is measured from the ABS control unit harness side connector T25/1 and the lower 25/2 end to 1.02 K ohm, normal. Turning the left front wheel, there is a 256 mV AC voltage signal between the 2 terminals. This eliminates the possibility of sensor and its line fault, and the suspect is concentrated on the internal circuit of ABS control unit. The shell of the control unit is split, and the corresponding solder joints of the G47 are found according to the direction of the circuit board interface circuit, and cracks are found in the solder joints. Troubleshooting: repair solder joints, install control units, troubleshooting trial run.