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The FAW Pentium CA7165AT4 distinguished car with a mileage of about 142 thousand km. The owner reflected that the car had an impact from the 1 block to the 2 block and had an impact from the 3 gear to the 2 gear. Fault diagnosis: after the car first test to verify the fault phenomenon, in the normal course of the vehicle, from 1 to 2 gear and from 3 to 2 gear, there are obvious shift impact, but other gears are normal. According to the structure principle of the automatic transmission, the automatic transmission control unit (TCU) takes the signal of speed, engine speed, input and output shaft speed, throttle opening, engine load and so on. According to the shift control program control the switching and closing of the shift solenoid valve S1 and S2, the hydraulic oil is changed to change the hydraulic oil. The road is broken, the 1 block engine brake operation and shift operation are carried out, and the solenoid valve SLC1, SLC2, SLC3, SLB1 control the hydraulic pressure linearly according to the signal output from TCU, used to control the hydraulic pressure of the clutch C1, C2, C3 and brake B1, change its working state and control the planetary gear mechanism to achieve the smooth shift of the automatic transmission. The analysis shows that the possible reasons for the above failure are ATF low oil level or deterioration, low pipeline pressure, TCU to automatic transmission line harness, blocking or damage of shift solenoid valve, control of valve internal blockage, TCU damage and so on. According to the difficult and difficult fault diagnosis principle, first check the ATF oil level and quality, according to the oil position inspection method provided in the automatic transmission maintenance manual of the vehicle (use F-ADS fault detector to check the ATF oil temperature and ensure that the vehicle is placed on the horizontal ground at 35 to 45 C, change the shift lever to the P gear and do not start the start. " Machine, remove overflow valve and plug plug, check the overflow valve and filling plug, check whether'ATF overflow from the overflow hole, if ATF does not overflow, add ATF until overflow; start the engine, check whether ATF overflow from the overflow hole, if ATF does not overflow, add ATF until overflow, and ATF cooling to below 35 degrees, step on the brake pedal, in P block to D gear block block. Inter position shift, and at least 2S in each block, after 2 shifts to return to the P gear, ATF oil level in the normal range, and the overflow of the ATF color pink, bright, no impurities, normal; at the normal ATF temperature, the use of the pressure gauge automatic transmission line pressure, slack speed, the D gear pressure of the pipeline is 390 kPa (gauge). The fixed value is 337 kPa to 437 kPa), the pipe pressure of the R gear is 600 kPa (the specified value is 508 kPa to 643 kPa), and the pipeline pressure of the D gear is 1295 kPa (1295 kPa to 1500 kPa) at the stall, and the pipeline pressure of the R gear is 1890 kPa (the specified value is 1875 of 2106 to 2106), normal; measured the terminals to automatic change. The corresponding wire connector of the speed device corresponds to the line between the terminals, and the resistance of the shift solenoid valve is measured by a multimeter. The resistance of the SLC1 is 5.50, SLC2, SLC3, SLB1, and the resistance of the lock control solenoid valve SLU is 5.3 Omega, the resistance of the electromagnetic valve SLT is 5.6 Omega, and the prescribed electricity of the solenoid valves. Resistance of 5 Omega to 5.6 omega (20 degrees C), all normal; check the valve body, found the shift electromagnetic valve SLBI internal reset spring fracture, other mechanical valves normal, no foreign body. Troubleshooting: because the shift solenoid valve SLB1 reset spring breaks, and the shift solenoid valve SLB1 is not provided by separate parts, only the control body assembly can only be replaced (the part number is FS5021100A). Replacement of control valve assembly after trial run, gear shift impact failure, troubleshooting.