The mileage is about 55 thousand km, with a 2.5 L engine and a cvT transmission in 2012 to import the Reno Leo sports utility vehicle. User response: when the vehicle is sometimes turned off, even if all the power is shut down and the door is locked, the 4 door lights will also be Chang Liang. Inspection and analysis: the maintenance personnel through the inquiry learned that the vehicle had been overhauled in another 4S shop before the fault, but did not find the cause of the failure, only to open the road test again. After the maintenance personnel receive the car, it is found that the door switches of the front passenger side door can not turn the door lights off, and the door lights of the 4 doors are still always bright after the door switch on the 4 door frames is moved one by one. Therefore, the maintenance personnel suspect that the front door of the front passenger side door switch has a problem, so the replacement, after the replacement, repeated test, failure phenomenon no longer appear. But after the delivery of the vehicle to the customer for a period of time, the customer calls to reflect on the rain or after the car wash, the 4 door lights have always been on the phenomenon of trouble still appear. Accordingly, the maintenance personnel judged that the malfunctioning vehicle may be suffering from "joint disease", which may be caused by the insertion of a connector in a system. After the maintenance personnel reconnect the car to verify the fault, use the car washing equipment to the front of the front passenger side door of the door switch near the local flush, when washing the car has another maintenance personnel, let it observe the light of the car door light. After flushing the front passenger side door for nearly 3 min, the failure phenomenon did not appear, so it was changed to the door switch of the left rear door for local flushing, and the failure phenomenon occurred again. The failure and then try to turn on and close the left rear and right rear doors respectively. The failure phenomenon shows that the inkstone from the above failure phenomena and the inspection process can be learned that the possibility of the above failure caused by the intake of a certain connector in a system is objective. When the fault disappears after the first replacement of the front passenger side door switch, the maintenance staff will focus on the related harness of the front passenger side door. In order to further verify the previous judgment, the maintenance personnel dismantled the door lights of the front passenger side door, measured the power line of the door lamp in the case of opening the door, confirmed the power supply of 12V, and the iron wire was normal, which again proved that the fault was accidental again. By observing the circuit diagram related to the door lamp of the car, it is found that the door lights are controlled by the body control unit. The door switch sends the door opening and closing signals to the body control unit, and the car's door lights are lit and extinguished by the body control unit. In this way, if any of the car door lights in each vehicle door is connected with the body, it will cause the occasional fault. Then after measuring the undiscovered problems, first, the wire harness of the front passenger side door is removed, the inner trim of the door is dismantled, the wire harness of the door switch is disconnected, and the wire harness of the door lamp is checked gradually. It is found that the spot of the contact between the car door lamp and the metal material of the door has been worn out, and the copper wire of the car door lamp wire harness has already been found. Oxidation and corrosion. Troubleshooting: repair the damaged wiring harness, then wash the vehicle repeatedly for trial run. Before the fault is no longer appear, the trouble is completely eliminated. Review and conclusion: the failure to exclude the fault left a very deep impression on the maintenance staff. The vehicle failed to travel to 2 4S stores in a very short time. The first time to the store did not check the cause of the failure; after the second to the store to replace the front passenger side door switch after the temporary removal of the fault, but did not continue to carry on the failure of the cause of the deep excavation; and the third time to the store, driving the vehicle is not the customer himself, can not tell the maintenance personnel the failure situation clearly. However, the maintenance personnel did not make inquiries due to negligence to understand the characteristics of the failure. This leads to avoidable rework, which will eventually lead to customer dissatisfaction and complaints. Therefore, it is necessary for the maintenance personnel to obtain the time, place, environment and fault characteristics from the customer before the maintenance. These factors have an indispensable role in the trouble shooting.