The mileage of more than 200 thousand km, equipped with 09G automatic transmission in 2008 imported the 2.0TSI automatic Alltrack wagon. The car was overhauled by the other 3 repair blocks because of the slip of the 4 gear. At that time, after the disassembly inspection, the transmission clutch's disposable piston was damaged. Replacement of disposable piston, automatic transmission repair kit and oil filter parts. After running for half a year after maintenance, there was a phenomenon of shifting, skidding, locking and completely unable to drive. Inspection and analysis: after the maintenance personnel receive the car, the fault diagnosis is carried out with the fault diagnosis instrument, and the fault code of the transmission control unit is read by the P0734-4 speed ratio error. Check the oil quality of the transmission and find the smell of coke. Road test confirms that there is a slip phenomenon in the transmission, and the vehicle can not rise to 4, 5 and 6 gears. Remove the transmission from the vehicle and check the K2 clutch oil pressure with the static oil pressure tester, which is 140 kPa, far below the standard value of 700 kPa. The disassembly gearbox found that the K2 clutch had been seriously ablated, and the friction piece almost turned into the inner tooth steel sheet. As we all know, for all wheel driven vehicles, such as the Volkswagen import car, even if the transmission gear shift skidding exceeds 1000 r/min, it will not ablt the clutch friction plate. However, the K2 friction disk of the car is ablated, which indicates that the internal oil passage of the transmission must have severe pressure relief. Take out the clutch drum and check that the Teflon ring replaced by the last maintenance has been seriously broken and deformed. The cause of the failure of the transmission and the failure of the transmission is that the abnormal wear and tear of the clutch caused by the abnormal wear and tear of the Teflon ring resulted in the slipping and erosion of the clutch, which caused the failure of the vehicle to lock and shift the gear. Troubleshooting: changing the transmission package and the already ablated K2 clutch friction plate according to the overhaul program, and carefully cleaning the other internal components of the transmission, and completely eliminate the failure of the loading road test.