Suspension Control ( Automatic - Electronic ): Description and Operation

NOTE: Starting in 1990, there were four separate models of sedans: XJ6, Sovereign, Vanden Plas, and Majestic. There was no Majestic for 1991.

Hydraulic System 1990-92:

The 1990-92 sedans (except XJ6 model) equipped with the central power hydraulic system, use the system to provide ride leveling only. The system shares a reservoir with the power steering system and both use HSMO (hydraulic system mineral oil).

Up to VIN 653345, the valve block charge port to the earlier brake boost accumulator, is blocked off. The charge and up valves operate together to pressurize the rear struts.

From VIN 653345, the valve block is the same but the up valve is deleted.

Valve Block Up To VIN 653345:

Up to VIN 653345, the operation of the three valve block solenoid valves is controlled by the ride height sensor only. Both the charge and up valve solenoids are activated by the ride height sensor via the suspension relay. The down valve solenoid is activated directly by the ride height sensor.

From VIN 653345, the up valve is deleted and replaced by a plug. The operation of the charge down valves remains the same as above.

No Ride Leveling Operation / No Accumulator Charging:

When there is no call for ride leveling pressure, the charge valve is open, directing oil flow back to the reservoir. The up and down valves are closed to the ride leveling circuit.

Ride Level Up Operation:

When ride leveling up pressure is required, the charge and up valve solenoids are activated to close the charge valve and open the up valve in vehicles up to VIN 653345. In vehicles from VIN 653345, the charge valve solenoid is activated to close the charge valve. Pressurized oil is directed to the ride leveling circuit to raise the rear of the vehicle. When the ride leveling compensation is achieved, the up valve closes and the charge valve opens directing oil from the pump to the reservoir.

Ride Level Down:

When ride leveling down is required, the down valve solenoid is activated to open the down valve allowing oil return to the reservoir to lower the rear of the vehicle. The trapped line pressure valve located within the down valve, maintains a minimum pressure in the rear suspension.