Inputs and Outputs

The Air Suspension/EVO Steering Module controls both the Air Suspension System and the EVO Variable Assist Power Steering System.

The Air Suspension System is designed to maintain the rear end height of the vehicle within predetermined limits, even though passengers may enter or exit the vehicle and objects may be placed in or removed from the trunk.

Vehicles equipped with the Air Suspension System do not have conventional coil springs placed between the rear axle housing and the frame. Instead, inflatable air springs are placed there. The air springs are inflated or deflated by a compressor/vent solenoid assembly that is controlled by the 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.

Short Term

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.

Long Term

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 and computes an average vehicle height. The Module adjusts vehicle height only when the average height is not within the predetermined limits.

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

MODULE INPUT

Air Suspension Switch

The Air Suspension Switch turns the system on and off during repair and/or diagnostic procedures.

Door Jamb Switches

With any door open (or ajar), battery voltage is present on circuit 24 (DB/O) at the Module. With this signal present, the Module will not lower the vehicle. This will prevent an open door from being lowered onto a curb or other object.

The Module ignores a "door open" signal if vehicle speed is above 15 mph.

Linear Height Sensor

The Linear Height Sensor determines whether or not the vehicle rear height is within predetermined limits. The Air Suspension Module supplies power and ground to the Sensor and then monitors the signals it gets back on circuits 427 (PK/BK) and 428 (O/BK). The Height Sensor can indicate only three conditions: vehicle trim height, vehicle above trim height and vehicle below trim height.

Vehicle Speed Sensor

The Vehicle Speed Sensor input is used for both the EVO Steering and the Air Suspension System. In the Air Suspension System, the Module uses the input to determine whether the vehicle is stationary, moving below 15 mph or moving above 15 mph.

MODULE OUTPUTS

Air Spring Solenoids

Each air spring has a replaceable Air Spring Solenoid. This Solenoid operates a valve that blocks air from entering or leaving the air spring. The Air Spring Solenoid windings are grounded by the Air Suspension/EVO Steering Module when air must be added or removed form the air springs.

Vent Solenoid

The Vent Solenoid is located inside the Air Suspension compressor. When energized, the Solenoid operates a valve that allows air released from the air springs to be vented.

Compressor Relay

Voltage is present at the Compressor Relay coil at all times. The Compressor Relay coil ground circuit is controlled by the Air Suspension/EVO Steering Module. When the Module grounds the coil, the Relay contacts close and power flows to the Air Suspension compressor Motor.

Warning Indicator

If the Air Suspension/EVO Steering Module detects a system fault, it grounds circuit 419 (DG/LG)) to the Instrument Cluster and the AIR SUSPENSION Indicator turns on. The Indicator also blinks whenever the Compressor Relay is energized.

Raising the Vehicle

To raise the vehicle, the Module first grounds circuit 420 (DB/Y) to energize the Compressor Relay and start the Air Suspension Compressor. After a one second delay, the Module energizes the Air Springs Solenoids. Compressed air flows from the Compressor into the air springs until the Module determines, from the Linear Height Sensor, that the vehicle has reached trim height. The compressor is then shut Off and the Air Spring Solenoids are de-energized.

Lowering the Vehicle

To lower the vehicle, the Module energizes the Air Spring Solenoids and the Vent Solenoids at the same time. Air escapes from the air springs and the vehicle lowers. When the Module determines that trim height has been reached, all three solenoids are de-energized.