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A Lexus IS200 car with a mileage of about 100 thousand km and a A45 DE automatic transmission. User response: the car is difficult to start. Once it starts, it will be normal to drive. After receiving the car, the engine system is checked, the engine runs smoothly, the idle speed is 750r/min, the engine power is strong when the engine is accelerated, the engine warning light of the dashboard is extinguished normally, indicating that the engine system is normal. Basic inspection of the automatic transmission system, automatic transmission oil and oil quality is normal, indicating that the internal friction of the automatic transmission does not burn. On the road test, put the transmission rod in the D position, release the brake pedal, the vehicle does not go forward, step down the accelerator pedal, when the engine speed reaches 1800r/min, the vehicle is slow to drive. When the speed gradually increases, the automatic shift function is normal. Reverse, normal. The transmission lever is placed in the L position and the vehicle starts to start normally. The stall test was carried out. The maximum engine speed of the engine at D position was 2200r/min, indicating that there was no slippage of the executive element in the range of the standard value (2050 ~ 2350r/min). Referring to the implementation element worksheet, it is found that when the transmission lever is placed in the D position, the actuating elements that transmit torque include the overspeed direct gear clutch, the overspeed one-way clutch, the forward gear clutch, the 2 one-way clutch, and so on. When the transmission lever is in the L position, the actuating elements that transmit the torque include the overspeed clutch and the overspeed one-way clutch. The device, the forward gear clutch, the low / reverse brake, the No. 2 one-way clutch and so on, because the low / reverse brake and the No. 2 one-way clutch are in parallel connection, so the No. 2 one-way clutch FZ acts but does not transmit the force. The vehicle started normal in the L position, indicating that the overspeed direct gear clutch, the overspeed unidirectional clutch and the forward gear clutch are normal. Therefore, it is inferred that the No. 2 one-way clutch has trouble. The automatic transmission is decomposed and checked. It is found that the one-way clutch of 2 is damaged, that is, the one-way locking function is invalid. Replacement of No. 2 one-way clutch, the fault is completely eliminated. 2 one-way clutch slipping causes D1 gear to start difficult, but will not cause damage to other parts, so the automatic transmission oil is very clean, and the automatic transmission control unit has no related fault code. When this kind of repair work is carried out, the cause of failure should be analyzed in combination with the working table of the components, and the pertinence inspection is made to the components that may have faults, thus improving the success rate of maintenance.