Suspension Control ( Automatic - Electronic ): Description and Operation

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DESCRIPTION
WARNING: BEFORE SERVICING ANY AIR SUSPENSION COMPONENTS, TURN AIR SUSPENSION SWITCH OFF OR DISCONNECT BATTERY GROUND CABLE TO PREVENT VEHICLE DAMAGE OR PERSONAL INJURY.

The rear air suspension:
- is an air-operated, microprocessor-controlled, suspension system.
- replaces the conventional rear coil spring suspension.
- provides low spring rates for improved ride and automatic rear load leveling.
- is standard equipment.

The rear air suspension system has the following features:
- The system is operational with the ignition switch in the RUN position.
- Automatic rear load leveling has limited operation for one hour after ignition switch is turned to OFF.
The air suspension switch, located on the RH side of the luggage compartment, must be turned OFF when the vehicle is on a hoist, being towed or jump started.
The CHECK AIR SUSPENSION warning indicator is located in the instrument cluster, to the right of the speedometer.
- The warning indicator flashes five times and then stays on with ignition switch in the RUN position and the air suspension service switch turned off or when a system malfunction is detected.
The rear leveling system operates by adding or releasing air in the rear springs to maintain the level of the vehicle at a predetermined rear suspension ride height dimension, and is controlled by a control module.
- The rear air suspension control module also controls the electronic variable orifice (EVO) power steering. Description and Operation of the EVO power steering system.
Air required for leveling the vehicle is distributed from the air compressor to the rear air springs by a nylon air line which runs from the compressor air drier through a Y-fitting to each individual rear spring.

OPERATION
Weight Added
When weight is added to the vehicle the air suspension system responds as follows:
- The air suspension height sensor length is reduced from trim length, sending a "rear is low" signal to the control module.
- The control module then turns the compressor on by grounding the compressor relay control Circuit 420 (DB/Y). This restores the rear of the vehicle to trim position.
- B+ is supplied to the relay coil by Circuit 414 (O/R).

- The control module opens the spring solenoid valves by switching Circuits 1114 (BR/PK) and 1115 (T/W) to ground. This allows pressurized air to enter the rear springs.
- B+ is supplied to the air spring solenoid valves by Circuit 414 (O/R).

- Compressed air flows from the compressor through the compressor air drier air lines and spring solenoid valves into the rear springs.
- As the rear springs raise the rear body height, the air suspension height sensor increases in length until the preset trim height is reached.
- The control module then turns off the air compressor (through the relay) and closes the air spring solenoid valves.

Weight Removed
When weight is removed:
- The air suspension height sensor length is increased from the trim length, sending a "rear is high" signal to the control module.
- The control module then opens the vent solenoid valve (located in the air compressor by switching Circuit 421 (PK) to ground and opens the solenoid valves by switching Circuits 1114 (BK / PK) and 1115 (T/ W) to ground. This restores the rear of the vehicle to trim position.
- Compressed air flows from rear springs, through the air spring solenoid valves, air lines, compressor air drier, and out the vent solenoid valve.
- As the body lowers, the air suspension height sensor length decreases until the preset trim height is reached.
- The control module then closes the vent and solenoid valves.