A Lexus LS400 car equipped with a 1 UZ-FE engine and a A341 E automatic transmission. Previously, the automatic transmission slipping fault was disassembled and repaired, resulting in the vehicle being unable to drive. Failure analysis: this kind of fault is divided into no file, no forward gear, no reverse gear or missing gear (lack of 1 or several gears) and so on. If the vehicle is unable to drive at any driving gear, the fault factors outside the automatic transmission system should be first checked, such as the wheel is locked, the transmission system is stuck, and the transmission system parts are damaged, all of which will lead to power interruption. If the mechanical locking problem of the power output part of the automatic transmission (the lock mechanism does not remove the pawl), the automatic transmission will be unpowered. The routine maintenance methods are as follows: put the transmission rod in the N position, unlock the parking brake, check whether the vehicle can drive the vehicle on the flat ground, lift the vehicle, check whether the wheel can rotate, and whether the drive shaft can rotate with the driving wheel. If the above check results are normal, then the fault can be judged in the automatic transmission itself. The actual inspection results show that there is no problem with the external mechanism of the automatic transmission. The gear lever is attached to all gears, resulting in no vibration of the automatic transmission, and the vehicle can not drive. There is no sense of vibration in the hanger indicating that the hydraulic system is faulty, such as hydraulic torque converter, oil pump, hydraulic valve body damage or oil pressure leakage. Check the automatic transmission oil, oil and oil quality is normal, indicating that the internal parts of the automatic transmission have no burnout fault. Check the transmission lever mechanism, normal. The working oil pressure of the automatic transmission is measured, and the working oil pressure is obviously low, which indicates that there is leakage inside the automatic transmission or the damage of the oil pump itself. Open the automatic transmission oil pan for inspection. It is found that the manual shift valve on the hydraulic valve body is not installed correctly and is not attached to the shift fork. Install manual shift valve, test run, trouble shooting. The hydraulic oil output from the oil pump of the dynamic transmission is transmitted to the hydraulic torque converter to lock the parts such as the relay valve, the main pressure valve, the manual shift valve, the throttle valve, the accumulator valve and other components. If the manual shift valve is not installed, the hydraulic oil will flow directly into the oil pan, the oil pressure can not be established, and the other hydraulic valves and the actuating elements can not be operated. The result is that there is no failure to respond to any file.