Failure phenomenon: a Chery QQ car (the remote control has automatic window function), the appearance of the right rear window is sometimes uncontrolled. After the window is lifted up, it will automatically drop down. Fault diagnosis: after receiving the vehicle, the basic inspection is carried out first. After the ignition switch is switched on, the windows work normally and there is no hysteresis. Then the 4 window glass all down and then disconnect the ignition switch, and sit in the car, press the lock button, about 2S, each window automatically rises to the top, normal. Press the unlocking button to switch on the ignition switch, and the 4 window glass rises or falls normally. The car owner reflected, the fault appeared half a month ago, but there was no law to say, sometimes it did not appear for several days, sometimes 1 days will appear many times, the frequency is higher in the last few days; when the car is running normally, the window glass will automatically drop down, and the fault is not much close to the good or bad of the road condition. There is a possibility of good or bad road conditions. To find out the line diagram related to the window and lift in the maintenance manual, it is found that the car window lifting control principle, similar to the Chery A5 sedan and the Shanghai Huapu car, are controlled by the car body anti-theft module, such as the need for the window to rise, as long as the wire that controls the car window. According to the analysis of the circuit diagram, the right rear window will fall automatically, indicating that the signal on the rear window lifter switch has been lowered to the car body anti-theft module. Use the multimeter to check the window control switch according to the circuit diagram, nor do you find any abnormalities. Then the owner reflected a valuable clue: with the remote control lock, the right rear window will come down after the ignition switch is turned on. As the car owners say, this shows that the lift and the ignition switch connected, but according to the maintenance manual, there should be no relation between the two. It seems that the problem is still on the related line. Because the door switch is more frequent, so the main door wire harness is the most easy to get out of the problem, so the left wing plate is removed, pull out the main car door wire harness, remove the end of the package layer, visual inspection, without any breakage, gently pull the end, can be heard to a relay work sound. At this time, let the colleagues gently pull the main door outside the end of the door, I listen carefully in the driver's cab again, at the same time carefully check the left side of the wiring harness of the place, found to pull the end gently, there is an end connector fell off. Troubleshooting: after the end of the shedding is carefully inserted and tested, the above failures will disappear. After 1 months of follow-up visits, the failure has not appeared. It seems that the main car door ended with a malfunction caused by the poor contact of the connector.