The mileage is about 50 thousand Km, and the model is CD340's 2012 Changan Ford S-MAX commercial vehicle. User response: the car wiper sometimes acts on its own during driving. Inspection and analysis: through communication with the users, the maintenance personnel learned that this situation only happened 2 times. When the vehicle was running, the wiper began to turn without any action. After scraping for several times, the wipers returned to normal. According to the result of inquiring, it is judged that the fault is intermittent fault. Using IDS to self diagnose the vehicle, the historical fault read almost covers all the system of the whole vehicle without judging the truth or false. Clear the fault code and re diagnose it. All the control units are normal. Fault is not reproduced by shaking the wiring harness and related connectors. Further check wiring harness of combination switch unit, wiper motor and vehicle body control unit. No problems were found. At this point, the maintenance personnel did not know how to reproduce the fault and the maintenance was deadlocked. At this time, an important clue was discovered through conversation with the driver. According to his recollection, the last fault occurred at high speed overtaking. Is the voltage too high? There is no problem in checking the power generation of the generator. Check the battery and combination switch and body control unit power supply and tie up, still no problem. Finally, when the tie line of the combination switch is dismantled, it is found that the joint surface of the G6D139 fixed bolt is yellow and yellow, and the tightening torque of the bolt is not enough. The problem should be found here. This tie point is also a variety of indoor lights, combined meters, seat heating, remote control receiver and blower control unit of the tie line. The analysis shows that when the charging voltage changes and the current of the tie - up point increases, the original circuit breakage is produced in the place where the contact is bad, which causes the failure of the combined switch. After the body control unit enters the emergency mode, the wiper starts to act, and the iron wire will soon resume conduction under the action of the electric spark, and the failure phenomenon will disappear. Troubleshooting: clean up the contact surface of the tie line and tighten the retaining bolt. Timely return to the user after the transfer, that the fault never happened again.