A Audi A6L car with mileage of about 116 thousand km and engine and transmission type of BDW and 01J respectively. Customer response: the trunk lid of the car is sometimes unable to lock. Fault diagnosis: after the car to the store, using the remote control to try to open the trunk, it is true that, as the customer said, open and close all do not play a role, and when good time and bad, even if the rear case does not function, the other 4 doors can also lock the lock, and the left rear tail light is not controlled by the light switch. Diagnostic instrument ODS detected the following faults: 1. case cover lock motor V53 electrical fault; 2. tank cover lock motor V155 electrical fault; 3. left terminal power supply circuit electrical fault; 4. left brake light bulb circuit breaker or to ground short circuit; 5. right brake light bulb circuit breaker or to ground short circuit; 6. left astern bulb circuit breaker or Short circuit to the ground; 7. right side reversing bulb to open circuit or short circuit to ground. Analysis: this car should be a typical circuit fault. The above execution elements are controlled by the comfort system control unit J393. The 1. control unit itself has a problem that can not work properly; the 2. control unit itself power supply or iron lap problem; 3. actuating element problem; 4. the subsystem control unit of its main control unit has problems. The result of the guided fault inquiry is that the J393 control unit needs to be replaced when the power supply and the tie up are normal. 1. use the multimeter to measure J393 power supply to 12.36V, normal, and the iron is normal; 2. after trying to replace the central door lock motor V53 in the rear cover, the failure is still still; 3. dismantled J393 found the corrosion phenomenon, the replacement method will replace the J393 of another car after the failure, so the order replacement J393, when the goods are replaced, when the replacement found the fault is still, when the replacement found the malfunction remains, when the replacement found the malfunction is still, after the replacement of the goods, found the faulty is still, after the replacement of the goods, when the replacement found the malfunction remains, after the replacement of the goods, to find the faulty still, after the replacement of the goods, when the replacement found the malfunction, after the replacement of the goods, still, when the replacement found the malfunction, after the replacement of the goods, remains the same. When the goods are replaced, the malfunction remains still found after replacement of the goods. Good time and bad; the 4.J393 control unit's system is to control the sunroof motor, check the circuit diagram to find the LIN line, and break with j393, the fault is still. Maintenance has been in a stalemate for a long time. It should be caused by so many reasons. Maybe some links have not been repeatedly verified and there are paper leaks. Then re check, when making a guide fault query with fault code 2 as the guide, found the reason, the current display: the left power terminal voltage is currently 3.8V, and when the wire harness is found when the voltage is sometimes 12.38V, that is, the power supply has a virtual connection. Under repeated verification, the gap of the base of the power supply insurance SF7 of the control unit j393 is too large to cause virtual connection. Finally, move the SF7's Insurance position. After commissioning, all tests were resumed. After release component protection, all fault codes are accidental. After cleaning, all the test cars are normal. Turn in, return visit a few days later, normal. Fault summary: this vehicle has two fault reasons, but there is only one fault. I can think of it, not to be able to do it. We must be rigorous and accurate in validating our own views and ideas.