Suspension Control Module: Description and Operation

The Air Suspension/EVO Steering Module continuously receives inputs from the Vehicle Speed Sensor (VSS), the Door Courtesy Lamp Switches and the Linear Height Sensor and maintains vehicle height by controlling two air Spring Solenoids, one Vent Solenoid and one Compressor Relay.

Compressor Relay

To raise the vehicle, the module turns on the Compressor through the Compressor Relay. After a one second delay, the desired Air Spring Solenoids are also turned on. The condition is maintained until the module determines, through the Linear Height Sensor, that the vehicle has reached the desired (trim) level. The Compressor Relay and Air Spring Solenoid then turn off.

The vehicle is lowered in much the same way, except the Vent Solenoid is turned on in place of the Compressor Relay, ignoring the one second delay.

The door courtesy lamp switch input is used to indicate whether or not a door is open. The system will not lower the vehicle if a door is open.

Air Suspension/EVO Steering Module

The Air Suspension/EVO Steering Module is programmed with two height correction strategies: a short term (immediate) correction strategy and a long term (averaging) strategy. If the Ignition Switch is in RUN, the vehicle is not moving and a door is opened or closed, the short term strategy is used.

The Module checks vehicle height and adjusts it immediately, according to Linear Height Sensor input.

If the Ignition Switch is in RUN and the vehicle is moving, the long term strategy is used. The Module monitors the Linear Height Sensor input and computes an average vehicle height. The Module adjusts vehicle height only when the average height is not within the predetermined range.

With vehicle speed above 15 mph, the Module ignores the "door open" input and follows only the long term strategy.

Air Suspension Switch

The Air Suspension Switch turns the system on and off during repair and/or diagnostic procedures. The CHECK AIR SUSPENSION Indicator signals the driver when a problem exists in the system. The CHECK AIR SUSPENSION Indicator is also used for diagnostic procedures.