Principles Of Operation

Vehicle Dynamic Suspension

Principles of Operation

WARNING: Shut off the electrical power to the air suspension system prior to hoisting or jacking an air suspension equipped vehicle. Failure to do so may result in unexpected inflation or deflation of the air springs, which may result in shifting of the vehicle during these operations. Failure to follow this instruction may result in serious personal injury.

WARNING: Any air spring which is unfolded must be refolded prior to being installed in a vehicle. Refer to the procedure. An incorrectly folded air spring could rupture, altering the handling characteristics of the vehicle. If a vehicle has been driven with an incorrectly folded air spring, a new air spring must be installed. Failure to follow these instructions may result in serious injury to vehicle occupant(s).

WARNING: Inspect the air spring for correct shape after it has been inflated with the wheels off the ground and the suspension unloaded. A deformed air spring could fail. Failure to follow this instruction may result in serious injury to the technician or vehicle occupant(s).

WARNING: Always inflate air springs before loading the suspension. If a load is applied to an uninflated air spring, the spring may be damaged and a new air spring will have to be installed. Damaged springs degrade vehicle handling, which could result in serious injury to vehicle occupant(s).

WARNING: Vent all air pressure from the air suspension system prior to disconnecting or removing any air suspension components. It is dangerous to remove air suspension components while under pressure. Failure to follow this instruction may result in serious personal injury.

The air suspension system is designed to improve ride handling and general vehicle driving performance.

Vehicle Dynamics Module (VDM)

NOTE: Before diagnosing the air suspension system, carry out the Vehicle Dynamics Module (VDM) self-test. If a DTC is present, follow the diagnosis and testing procedures. If no DTC is present, check the vehicle ride height by following the ride height adjustment procedure.
If the system cannot reach the correct ride height, check all of the air tubes and connections for leaks, blockage or damage, height sensor integrity and/or compressor relay operation before installing a new air compressor.

A microprocessor controls the air suspension system. The microprocessor and supporting hardware are contained in the VDM. The VDM responds to signals from various sensors in the vehicle to maintain the programmed ride height while the vehicle is either moving or stopped. The VDM accomplishes this by opening and closing solenoid valves to control the amount of air in the air spring(s). The VDM turns on the compressor by applying voltage through the compressor relay to inflate the air spring(s) and raise the vehicle. The VDM opens the vent solenoid to lower the vehicle by releasing air from the air spring(s) in response to signal inputs from the air suspension height sensor. The VDM has a preprogrammed trim height.

Air Suspension Switch

WARNING: Shut off the electrical power to the air suspension system prior to hoisting or jacking an air suspension equipped vehicle. Failure to do so may result in unexpected inflation or deflation of the air springs, which may result in shifting of the vehicle during these operations. Failure to follow this instruction may result in serious personal injury.

In the ON position, the air suspension switch provides a signal to the VDM which, in turn, deactivates the system. In the OFF position, the air suspension switch interrupts this signal to the VDM which, in turn, deactivates the system to maintain the vehicle height.

Air Compressor

NOTE: The compressor contains a thermal overload circuit breaker. The circuit breaker automatically resets after a cool-down period and after being tripped by excessive compressor motor heat.

The air compressor assembly consists of the compressor pump, electric motor vent solenoid and driver (must be installed as an assembly).

Air Suspension Rotary Height Sensor

One air suspension height sensor is mounted on the vehicle. The air suspension height sensor sends a voltage signal to the VDM. The output ranges from approximately 4.5 volts at minimum height (when the vehicle is low or in full jounce) to 0.5 volt at maximum height (when the vehicle is high or in full rebound). Install a new air suspension height sensor as a unit.

When the air suspension height sensor indicates that the rear of the vehicle is lower than trim height under normal driving conditions, the air compressor will turn on and pump compressed air into the air springs. When the sensor indicates that the rear of the vehicle is raised above trim under normal driving conditions, this will cause the air to be vented from the air springs to lower the vehicle back to its trim height level.

Solenoid Valve, Air Spring

WARNING: Vent all air pressure from the air suspension system prior to disconnecting or removing any air suspension components. It is dangerous to remove air suspension components while under pressure. Failure to follow this instruction may result in serious personal injury.

The air spring solenoid valve allows air to enter and exit the rear air springs during height adjustment operations. The air spring solenoid valve is electrically operated and controlled by the VDM.