GM Service Manual Online
For 1990-2009 cars only

The air suspension relief valve permits deflation of the rear suspension air springs. The air suspension relief valve is manually operated by the control valve switch located on the dash panel. The supply port on the relief valve closes when the control valve switch is actuated. This allows the air from the air springs to exhaust and the springs to deflate. The exhaust port closes and the supply air is directed to the air springs when the control valve switch is deactivated. The air springs are then allowed to inflate to normal ride height.