Inspection and analysis: the maintenance personnel test the car, found that the car in the moment of loosening the accelerator pedal, if it happens to meet the 1-2 and 3-2 shift points, then there will be a clear shift impact. Detection of engine and transmission control unit failed to find fault codes. Check the transmission oil, oil, normal. Looking at the adaptive values stored in the transmission control unit, it is found that the oil acceleration time of clutch C has reached 40 ms. This shows that if the compensation is not compensated, the clutch will be 40 ms later than the normal condition to fill the oil. This self adaptive value indicates that the oil passage of the clutch C is leaking, and when the 2 gear is replaced, the 1 clutch is put into operation. In the process of oil compensation, the first consideration of the control unit is to protect the mechanical parts, so gear shifting is difficult to guarantee. It seems that the problem is here. Troubleshooting: replace the clutch C, repeat the trial run, confirm that the trouble is completely eliminated.