Why did Passat shift to D? Sometimes the throttle seems to slip and the car can't get on.

1, check the automatic transmission oil. The oil quantity is normal but the oil quality is slightly black and slightly burnt. Time lag test, the result is normal. The measured oil pressure, oil pressure of D and R gears are all within the standard range. The stall test shows that the stall speeds of D4, D3, 2nd, 1 and R are all around 2300r/min, which is normal. Unplug the wiring harness plug of the shift solenoid valve, and measure the stall speeds of D4 and D3. The results are normal, indicating that there is no slip fault in each clutch of the automatic transmission. Self-diagnose the engine system and automatic transmission system with diagnostic instrument, and there is no fault code. After adjusting the throttle cable and carrying out a road test, the fault symptoms did not improve significantly.

2. Measure the signal voltage of the throttle position sensor. The signal voltage is 0. When the throttle valve is fully closed, it is 45V, and when the throttle valve is fully opened, it is about 4.5v.. When the throttle rotates, the signal voltage can change evenly with the throttle opening, indicating that the throttle position sensor is normal. Measure the throttle position sensor signal at D7 terminal of automatic transmission control unit harness plug. The signal is good and normal. Check the shift solenoid valve, locking solenoid valve, spindle speed sensor, auxiliary shaft speed sensor and other components, all of which are normal. Check the S-file program switch and its circuit, and no abnormality is found. Open the case of automatic transmission control unit (integrated with engine control unit) and check whether the circuit board is corroded or burned.

3. Lift the vehicle, start the engine, and put the shift lever into D4 to accelerate, but there are still delayed upshifts and instantaneous skidding. Keep the automatic transmission running in the third gear, unplug the wire harness plugs of the two shift solenoid valves, and the automatic transmission can quickly shift into the fourth gear without slipping, indicating that the fault lies in the electronic control part. The road test shows that it is necessary to accelerate to about 2800r/min to upgrade to the third gear, and the engine speed reaches 3000r/min to upgrade to the fourth gear, which has an instantaneous slip phenomenon. Press the S-shift program switch to activate the sport mode, thus realizing the delayed shift. Unplug the harness plug of the shift solenoid valve and manually shift the automatic transmission from second gear to fourth gear. As a result, the slip phenomenon disappeared, indicating that the electronic control system of the automatic transmission is faulty. Connect the LED to the harness plug of the lockup solenoid valve to lift the vehicle and accelerate it. When the vehicle speed reaches 90km/h, the LED lights up. Unplug the harness plug of the locking solenoid valve and measure the resistance of the locking solenoid valve, which is normal.

4. Check the electronic control system of automatic transmission, and the results show that the coolant temperature signal, throttle position signal, vehicle speed signal and engine speed signal are all normal. Check the solenoid valve circuit, power cord and ground wire of the automatic transmission control unit, and no problems are found. Replace automatic transmission control unit and carry out a road test. Instantaneous sliding phenomenon disappears, and the locking function of hydraulic torque converter fails. Put the gear lever in the D position, depress the brake pedal, and energize the torque converter locking solenoid valve. The solenoid valve makes an action sound, but the engine speed does not decrease obviously, and there is no jitter or flameout, indicating that the fault lies in the lock-up clutch or lock-up oil circuit of the torque converter. Replace the hydraulic torque converter and completely eliminate the fault.