Diagnostic Procedure 4

DIAGNOSTIC PROCEDURE 4

SYMPTOM: Abnormalities when stopping engine

NOTE:
When engine is stopped, the system operates to maintain system pressure at a fixed level (charged balancing pressure). First, the pump stops, eliminating the pump discharge pressure, which causes the main check valve to close. Simultaneously, the control level of the pressure control valve is gradually changed to the neutral pressure [5,002 kPa (51 kg/cm2, 725 psi)]. Because no oil is fed from the pump, the supply pressure flows out to the return pressure side via the pressure control valve. As a result, the supply pressure lowers gradually. When the pressure lowers to 5,002 kPa (51 kg/cm2, 725 psi), the operation check valve closes, shutting off the return pressure outlet. After the operation check valve closes, the supply pressure and return pressure gradually become equal (charged balancing pressure). Approximately 3 minutes after stopping the engine, the fail-safe valve and pressure control valve are de-energized, and no longer operational.

During the above-mentioned operation, some mismatching may occur between the operation of the hydraulic system and the electrical units due to the ambient temperature. The status of control is existing at the time the engine stopped. Such a minor mismatching should not be regarded as a problem. It is requested to fully understand the conditions and situations under which such mismatch occurs.
(1) If either battery terminal is disconnected or the active suspension fuse (No.17) is removed (within 3 minutes after stopping the engine), the vehicle height may change. This is normal. However, care should be taken when performing maintenance near the vehicle.
(2) Depending on the ambient temperature and pressure control valve status when the engine was stopped, some mismatching may occur between the operation of the hydraulic system and the electrical units. It creates a jerk of the vehicle body. This is normal.
(3) When ambient temperature is very low, vehicle height may drop a little about 3 minutes after stopping the engine. This is normal.
(4) When jacking up the vehicle, be sure to wait about 3 minutes after stopping the engine. The vehicle body may jerk a little after stopping the engine.
(5) If the engine is restarted promptly, the vehicle body may slightly jerk depending on the ambient temperature and loaded condition of the vehicle. This, however, is normal.