A 2005 mileage car with a mileage of about 100 thousand km and a CVT transmission. User response: the gear shift lever of the vehicle is put into reverse gear, the engine is jitter drastically, the speed decreases obviously, and the gearbox part has "rattle" noise. After receiving the car: after repeated checks, there are no abnormal connections between engine, transmission and body. It is suspected that the damping spring in the flywheel plate is broken, so the transmission and flywheel discs are removed to check the damping spring, and the result is normal. The disassembly of the transmission is checked, starting clutch, reverse clutch and related components are all normal. When the gearbox is loaded, the symptoms are gone when the car is tested and cold. The reason for the analysis is estimated to be related to the start clutch control procedure of ECM/PCM. Therefore, the starting clutch is calibrated according to the maintenance regulations. The specific steps are as follows: 1) starting the engine, allowing the engine to reach the normal working temperature (the cooling fan starts running). 2) turn on the headlights. 3) under the condition of no load, driving the vehicle at D position until the speed reaches 60km/h, do not step on the brake pedal, slow down the vehicle in more than 5S time (can pull down the parking brake to slow down, do not pull too fast to avoid an accident) until the vehicle stops. After the completion of the test, the fault is completely eliminated. Generally speaking, the problems of mechanical parts are usually doubted for abnormal sound failures. Such failures may be caused by the following case: disconnecting the battery cable, removing 20 fuse (15A) from the fuse / relay box below the dashboard, replacing the start clutch, replacing the control body, overhaul or replacement of the transmission assembly, overhaul or replacement of the engine assembly. These conditions may result in the loss of control data for the starting clutch of the ECM/PCM storage, the start of the clutch pressure control valve manipulation disorder, the repeated engagement and separation of the starting clutch, and the abnormal sound.