A Volkswagen Passat B5 car with a mileage exceeding 210 thousand km and a OIN automatic transmission. The measuring value of the main oil pressure is low after the overhaul of the car. Lift vehicles, test their gear shift quality is normal, but the road test has a slight skidding phenomenon, with this fault if the vehicle continues to drive, may appear serious burning, damage the transmission. Fault diagnosis: we have replaced oil pumps, overhaul bags (various pads and seals) during the overhaul of the transmission, and cleaned the torque converter and automatic transmission oil radiator. Pneumatic test has been performed on the actuators before installing the valve body, and no leakage of actuator oil has occurred. After assembling and loading, the main oil pressure at idle speed is measured. The D position is 3. 4bar and the R position is 5. 0bar, which is in line with the original factory specified value. Read the data flow in the road test, analyze the skidding phenomenon, and step down the accelerator pedal in the road test. There is a slight skidding feeling when one liter is a liter. In this case, the road test is not allowed, otherwise the fault will be enlarged. Recalling the replacement parts, in the assembly process have done a strict inspection, there will be no quality problems; the whole assembly process is relatively smooth, the clearance of the clearance have done strict measurement, will not lead to abnormal. Considering whether the influence of other control systems is caused, then the data flow of engine and other related data flow is analyzed, and the anomaly is not found, but the oil pressure of the transmission is adjusted. As shown in Figure 1, there is a plastic adjustment bolt at the end of the pressure regulating control valve on the gear valve body. The bolt is adjusted to the best position when the valve is out of the factory, and the new valve is generally not adjusted when the new valve is installed. According to the shape of the bolt slot, we can see that the outer edge of the bolt is designed to prevent the tooth from retreating. When the bolt is adjusted, the bolt can be swirled in clockwise. The adjustment result will increase the main oil pressure. When the bolt is rotated, the anti tooth locking bolt can not be back, and the special tool will be unlocked and the bolt can be swirled counter clockwise. After adjusting the adjustment bolt clockwise into the 1/2 ring, the D bit oil pressure of the idle speed rose to 3. 6bar. The road test vehicle still felt a slight skidding and the condition improved. Then, after several adjustments, the vehicle's idle speed was 4. 2bar, the road test vehicle was running normally, and after dozens of kilometers of road test, the car was all normal. (3) maintenance summary the design of OIN automatic transmission is low, and the requirements for oil pressure in operation are very strict. When the oil pressure is too low, the transmission often slips, resulting in premature damage to the transmission. In the actual maintenance process, if the parts and assembly are confirmed, the transmission valve can be adjusted properly with reference to the transmission oil pressure gauge to ensure the normal operation of the transmission. Comment on the system standard oil pressure value supplied by the manufacturer's maintenance data: the engine is 3.4 to 3. 8bar at idle speed. Although the actual measured values basically meet the requirements, they are still in a low position. In the strict sense, in the case that the oil pump actual pump oil capacity and mechanical components do not have a problem, it may still be a slight leakage of the system main oil road due to the slight leakage of the valve wear, so that the oil pressure is slightly in the lower limit, so that the light micro leakage can be made up by the method of adjustment. Since the adjusted oil pressure of the fault car is 4.2 bar, it is more able to indicate that the system oil pressure is still leaked. The automatic transmission can be used although the adjustment compensation (may be the requirement of the owner to save the repair fee), but the replacement body can restore the hydraulic system to the normal working condition.