A Honda accord with a mileage of over 200 thousand km, equipped with K20A7 electronic controlled engine and EAT40 automatic transmission. User response: the vehicle is braking at high speed, and the automatic transmission is downloaded immediately. The body vibration is obvious. After the car: self diagnosis of the engine system and automatic transmission system, no failure code. In trial, automatic transmission can shift automatically and the condition of the car is basically normal. This condition does not feel a problem for the ordinary driver, but the driver is more experienced and can feel the vibration caused by the drop of gear when the speed is slowed down (this process should not be reduced). After repeated test, it is found that when the vehicle is in the 5 gear, the braking is carried out, and then the speed is accelerated, the automatic transmission is first dropped to the 4 gear and then up to the 5 gear, which produces frequent shift to bring the impact. Observe the engine tachometer and speedometer of the dashboard, confirm that the engine's shift speed is slightly higher, which is estimated to be related to engine power shortage. Check the data flow of the engine system, the data are basically normal, but the throttle position signal is slightly larger: the throttle position of the idle mode is 9.07%, and the relative position of the throttle is 0%. Looking at the data flow of the automatic transmission system, the throttle position is also 9.07% without stepping on the accelerator pedal, which means that the data is taken from the engine system. Actually check the throttle position sensor and find that the sensor is adjustable. Loosen two fixed bolts, rotate the sensor, observe the data displayed by the diagnostic instrument, and tighten the fixed bolts when the throttle position changes to 4.72%. Road test, failure symptoms completely disappeared, maintenance work ended. This case illustrates the shifting principle of the automatic transmission. During shift, the gear control process is determined by two factors: engine load and vehicle speed. The position of the throttle reflects the engine load. The throttle position signal of the idle speed is an important reference signal. If the signal is too large, the signal of the throttle position in the partial load and the full load condition is also large, and the downward shift trend is larger at the same speed, resulting in the high speed shift. The relative position of the throttle is calculated by the engine control unit. The adjusted throttle position sensor signal will change, but after adaptive, the relative position of the throttle of the idling condition will still be 0%.