While checking some things, here is some reading info you may already know
The 4-Wheel Air Suspension (4WAS)
module commands changes in vehicle height that are necessary for both the load leveling and the vertical height adjustment features.
The 4WAS load leveling feature automatically makes adjustments in vehicle height so that the vehicle is always at trim height, and that constant front-to-rear vehicle attitudes are maintained over the load range of the vehicle. Adjustments in height that are necessary to correct height differences between the vehicle left and right sides for the 4WAS system are restricted to what can be reliably achieved with three height sensors.
The height adjustment feature has three vehicle heights within a two-inch span:
Kneel height-improves the ease of entering and exiting by lowering the vehicle one inch below the trim height in the front and rear when the vehicle ignition is in the OFF or LOCK positions and the vehicle is stationary.
Trim height-normal vehicle ride position; vehicle moves to trim position when the ignition is ON, when the transmission is initially shifted to DRIVE or REVERSE mode, when all doors are closed or when speed of more than 24 km/h (15 mph)
Off-road height-improves ground clearance by raising the vehicle one inch above trim height in the front and rear when the vehicle is at 4x4 low modes and the vehicle speed is less than 40 km/h (25 mph).
The 4WAS module uses the Universal Bus Protocol, (UBP)
, module communications network for sending and receiving various signals with the exception of speed, information from the three height sensors, and the air suspension
service switch. For additional information about UBP, refer to Module Communications Network.
The 4WAS system holds vehicle height when any door or rear hatch is opened. The system stores front and rear vehicle height the moment any door is detected open. The system then maintains this height regardless of the addition or removal of a load. The system returns to its commanded height when all doors are closed or vehicle speed exceeds 24 km/h (15 mph)