The automatic transmission failure lights on the instrument cluster have been flashing models: Dongfeng Citroen Fukang, equipped with 1.6L 16 valve engine, automatic transmission. The mileage is 128000km. Failure phenomenon: the user reflects the automatic transmission fault light (S and * key alternately flicker) on the combined instrument during the use of the vehicle, and the vehicle is obviously in a forced 3 gear mode of falling off operation (it is obvious that the vehicle's automatic transmission has no transmission ratio change). Fault diagnosis 1. PROXIA3 is used to control the engine control unit of the vehicle. The control unit of Shanxian County and the automatic transmission control unit is stored and asked to read the fault information. No fault information is obtained inside the engine control unit. The fault information read in the control unit of the automatic transmission is the pressure regulation fault. 2. check the oil level of the automatic transmission based on the previous maintenance experience (if the automatic transmission oil is too much or too little, it will affect the abnormal pressure in the internal hydraulic line of the automatic transmission system, causing the pressure regulation failure). The fuel plug on the upper part of the shell is added to the O.5L's new automatic transmission oil (AL4 automatic transmission designation automatic transmission oil). Start the engine, step down the brake pedal, stop the gear shift lever on each gear for a moment. After that, the automatic transmission shift lever is placed on the P gear position to let the engine run at idle speed. State • enter into the automatic transmission parameter measurement menu through the diagnostic instrument PROXIA3, and observe the oil temperature rising to 60 degrees centigrade to remove the oil surface of the lower part of the automatic transmission shell to check the screw plug. At the beginning, a small amount of oil is outflowing and then drops by drop. This indicates that the level of the automatic transmission is normal, and the pressure adjustment is also indicated. The generation of the joint failure is not related to the excessive and too little oil of the automatic transmission. 3. use the diagnostic instrument to read the automatic transmission loss counter under the setting menu of the automatic transmission control unit, and find its count value 32958, indicating that the new and old degree of the automatic transmission oil meets the requirements, and excludes the oil old of the automatic transmission. Exceeding the limit value causes the possibility of failure. 4. check the state of each solenoid valve (EVS1-EVS6, 6 sequential solenoid valves, pressure regulating electromagnetic EVM and torque converter lock solenoid valve EVLV) on the automatic transmission hydraulic control box, and carry out the exciting test operation of the related solenoid valve according to the prompt steps of the diagnostic instrument. The results obtained show that the PROXIA3 The working conditions of the 8 electromagnetic widgets are in line with the requirements. 5 check the working state of the oil pressure sensor and its working line. First, use the diagnostic line and Cambodia to lead out the various working feet of the automatic transmission, and then use the multimeter to measure the voltage value of the working feet of the oil pressure sensor in the two state of the ignition switch and the engine running. (the 24 feet, the sensor of the automatic transmission control unit connector, the sensor. The following results are obtained for the power supply foot, 55 foot signal feet, and 25 feet tiderfoot. The voltage of the 24 feet is 5V, the 55 foot voltage is 5V, the oil temperature of the automatic transmission is greater than 15 degrees, the automatic transmission gear shift lever is in the N or P gear, and the standard values of the feet in the normal condition are compared, and the signal foot is found to have problems, and then the ignition switch is opened and closed. The resistance value between the 55 feet and the 25 feet is measured below, and it is found that it is abnormal, the son is replacing a new oil to suppress the guard assembly, and then the fault deletions are carried out with the diagnostic instrument, and the road test operation is carried out. It is found that the automatic transmission fault lights on the combined dashboard are no longer flickering, and the operation of the automatic transmission under various operating conditions is also found. Return to normal. Fault summary: this fault is caused by the failure of the internal signal line of the automatic transmission oil pressure sensor which provides the main channel pressure signal to the automatic transmission control unit, resulting in the error of the main oil channel pressure signal provided to the automatic transmission control unit. In this case, the automatic transmission control unit is automatic. The oil pressure backup value is chosen to be calculated and controlled, and the work of the automatic transmission is in the downgrade mode (compulsory 3 gear), and the automatic transmission fault lamp glimpse of the automatic transmission on the combined instrument is lit to remind the users to carry out the maintenance of the automatic transmission system to the designated service station as soon as possible.