Air Suspension System Operation

NOTE:

The air suspension adjusts if the vehicle's doors are open, but the vehicle may not lower to its minimum setting.
A time delay may be evident before the vehicle reacts to the air suspension height request. The vehicle's systems need to be configured before each height adjustment.

Under normal operating conditions, the Chassis Control Module (CHCM) keeps the vehicle level at the 'current' ride height. The incoming height signals from the sensors are passed through filters to remove irregular signals produced by road noise or other irregularities.

When the vehicle is stationary or a height change is in progress, the signals are passed through a 'fast' filter. The 'fast' filter tracks the true rate of change of height. When the vehicle is moving, the signals are passed through a 'slow' filter. The 'slow' filtered signals remove almost all road noise from the signals and output a true long term average for each corner height. The 'slow' filtered signals cannot be used to respond quickly during height changes.

The CHCM monitors each corner height signal using the 'fast' filtered signals if the vehicle is stationary or the 'slow' filtered signals if the vehicle is moving. If the height remains in a 'dead band' which is ±9 mm from the target height, the control module does not implement any height adjustment changes. When the CHCM detects that a corner is outside of the 'dead band', the CHCM operates the compressor and/or the valves to move that corner back into the target height.

Cornering

If the CHCM registers a cornering force greater than 0.2g it will inhibit all height changes and corrections. The system will remain inhibited until the cornering force falls to less than 0.15g. The CHCM receives a message from the Restraints Control Module (RCM) on the High Speed (HS) Controller Area Network (CAN) chassis systems bus for the cornering force. The RCM incorporates the yaw rate lateral acceleration sensor.

Rapid Acceleration

If the CHCM registers a rapid acceleration greater than 0.2g it will inhibit all height changes and corrections. The system will remain inhibited until the rapid acceleration falls to less than 0.15g. The acceleration is calculated by the CHCM from the vehicle speed signal. The vehicle speed signal received from the Anti-Lock Brake System (ABS) control module via the HS CAN chassis systems bus.

Rapid Deceleration

If the CHCM registers a rapid deceleration smaller than - 0.2g it will inhibit all height changes and corrections.

The system will remain inhibited until the rapid deceleration rises above - 0.15g. The deceleration is calculated by the CHCM from the vehicle speed signal. The vehicle speed signal received from the ABS control module via the HS CAN chassis systems bus.

Air Suspension System Pressure

The compressor will not start if the system pressure is higher than 4 bar (58.01 psi).

Air Compressor Temperature

A temperature sensor is located within the air compressor to prevent overheating. If the temperature of the compressor cylinder head rises above pre-set limits, the CHCM will inhibit the compressor operation.