[Repair Case] Highlander 2nd to 3rd gear shock.
Posted by Tony Brown on
Model: Equipped with U151E/F automatic transmission.
Issue: Highlander 2nd to 3rd gear shock.
Diagnosis: When the vehicle accelerates hard, a forced downshift occurs from 3rd to 2nd gear.
As speed increases, and when the throttle is removed, the engine load is lessened. The vehicle will shift from gear 2 to gear 3 (the typical car upshift will be seamless if you don't step on the accelerator), but if you accelerate engine load will increase, and the engine and transmission computer will change gears. When overtaking, the car will automatically shift to a lower gear. If the U250E transmission is in 5th gear at this time, it will be reduced from 5th gear to 2nd gear when the accelerator is suddenly increased. It is normal for shocks to occur in this case. The following are some of the possible causes of a rough gear shift:
First, the transmission oil pressure is low, resulting in poor oil flow inside the transmission during rapid acceleration, resulting in bubbles, so the clutch cannot get enough oil pressure, and the combination is rough; the transmission is lacking oil; the oil is too dirty; the transmission filter is blocked; the oil pump has been used for a long time, and the wear gap is too large; the transmission is lacking oil; the oil is too dirty; the transmission filter is blocked; the oil pump has been used for a long time, and the wear gap is too large.
Second, the transmission's solenoid valve is malfunctioning; there is a procedure of switching between the brake B1 and the clutch K3. The brake B1 and the clutch K3 also interfere because the solenoid valve is decreased by the current's height and pressure. The pressure cannot drop swiftly when the solenoid valve is de-energized, which means the clutch K3 cannot be combined smoothly, creating movement interference between the clutch K3 and the brake B1, and the gear shift is rough. When the solenoid valve is activated, the pressure cannot rapidly rise, preventing the brake B1 from combining smoothly. Interfering with the movement of brake B1 and clutch K3, resulting in rough gear shifting.
Third, interference generated by changes in engine torque: the source of the impact is a problem with control time during the overlap shift, which results in an impact. When the engine shifts gears, the ignition time is delayed to minimize torque, resulting in smooth gear shifting. However, if the engine torque interference and the torque transmission of the shift box do not overlap at the same time, an impact occurs.
The fourth is with the transmission's internal actuators.
The actuators K1, K3, and B1 are involved in the process of moving from two to three gears.
The following are some of the possible causes of shifting storms: The space between the clutch and the brake is too large or too narrow, causing movement interference. The clutch is a moving component, and the moving oil generates dynamic pressure, which has a direct impact on clutch oil filling and unloading. After long-term operation of the clutch and brake, due to friction, grooves appear in the outer hub of the clutch, which will also affect the normal operation of the clutch and brake. According to the analysis, this phenomenon is normal and there is no malfunction, as shown in Figure 1 and Figure 2.