Principles of Operation

Rear load leveling maintains rear vehicle height. The system uses one height sensor, a steering sensor, and other vehicle sensors to measure driver and road inputs. The system maintains vehicle height on the rear axle through the use of an air compressor, two air solenoids, various air lines, and the use of an air spring integrated inside each shock.

Driver inputs include braking, throttle position, steering rate and position.

The rear load leveling system regulates the pressure in each air shock by compressing and venting the system air. Increasing air pressure (compressing) raises the vehicle. Conversely, decreasing air pressure (venting) lowers the vehicle.

The sensor sends a voltage signal to the air suspension control module. The output ranges from approximately 4.75 volts at minimum height (when the vehicle is low or in full jounce), to 0.25 volts at maximum height (when the vehicle is high or in full rebound). The sensor has usable range of 80 mm (3 inches) compared to total suspension travel of 200 - 250 mm (8 - 10 inches) at the wheel. Therefore, the sensor is mounted inside the wheels at a point where full suspension travel at the wheel is relative to 80 mm (3 inch) of travel at the height sensor. The height sensor is not repairable.

Note: The compressor motor contains a thermal overload circuit breaker. The circuit breaker automatically turns the compressor off if tripped by excessive temperature. The air compressor will operate normally after it is allowed to cool.

The air compressor assembly:
^ Consists of a single cylinder, electric motor driven compressor pump and vent solenoid; neither are repairable.
^ Is mounted above the spare tire in the rear of the vehicle.
^ Is powered by a relay, controlled by the air suspension control module.
^ Passes pressurized air through the air compressor drier that contains silica gel (a drying agent). Moisture is then removed from the air compressor drier when vented air passes through the drier and out of the system during vent operation.

The vent solenoid valve:
^ Is enclosed in the air pump head casting, which forms an integral valve housing that allows the valve tip to enter the pressurized side of the system.
^ Opens when the air suspension control module determines lowering is required.
^ Releases pressurized air when system pressures exceed safe operating levels.

The air suspension switch provides power to the control module in the ON (closed) position only. When OFF, the rear load leveling system will not function.

The steering sensor is mounted inside the passenger compartment on the steering column. It provides steering rate and position to the control module through two signals: Steering Sensor A and Steering Sensor B.

The rear fill solenoid connects the output of the compressor assembly to the two rear air shocks. When energized along with the rear gate solenoid, air pressure to the rear air shocks can be modified, affecting axle height relative to the body. The rear gate solenoid provides pneumatic isolation of the left and right sides of the vehicle, when lateral loads are detected by the air suspension control module and in response to steering and vehicle speed.

A microcontroller-based electronic air suspension control module controls the air compressor motor and all system solenoids. The module also provides power to the rear height sensor. The air suspension control module controls vehicle height adjustments by monitoring one height sensor, vehicle speed, a steering sensor, acceleration input, the door ajar signal, two transfer case signals, and the Brake Pedal Position (BPP) switch. The module also conducts all fail-safe and diagnostic strategies and contains self-test and communication software for testing of the vehicle and module.