Air Spring
WARNING: This page is about a different car, the 2003 Lincoln Navigator and 2003 Ford Expedition. However, it is still accessible from the selected car via links, so may be relevant.
The 4WAS system has front and rear air springs. The air springs provide a varying spring rate proportional to the system's air pressure and volume. The air suspension system regulates the air pressure in each air spring by compressing and venting the system's air. Increasing air pressure (compressing) raises the vehicle; decreasing air pressure (venting) lowers the vehicle. Vehicle height is maintained by the addition and removal of air in each air spring through an air spring solenoid installed in the upper spring cap and energized through the 4WAS module command.