A Audi A6L car with a distance of about 26 thousand km. User response: the vehicle is on the forward block and the car is not moving. The refueling door is serious and the reverse gear is normal. Fault diagnosis: using VAS5052 query, there is a fault code in 02 system: pressure control valve pollution / static, as shown in Figure 1. The current of the first area of the tenth sets of data streams is 0.430A, obviously larger. It is doubted that the spool box is damaged. According to past experience, try to replace the slide valve box. When dismantling the control unit of the transmission and the check of the slide valve box, it is found that the inner damage of the forward oil seal is found. The leakage may be due to the pressure of the forward oil seal. Then the forward oil seal and the transmission oil are tried to replace the test. The matching value of forward gear clutch characteristic curve is 0.2 ~ 0. 35A. Troubleshooting: replace advance oil seal and transmission oil, troubleshooting. Fault summary: usually in the replacement of the slide valve, the service station does not check or replace the oil seal, but in the ELSA maintenance manual, it is pointed out that the related oil seal should be replaced when the slide valve box is disassembled.