Circuit/System Description
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2007 GMC Yukon XL, 2007 GMC Yukon, 2007 Chevrolet Tahoe, 2007 Chevrolet Suburban, and 2007 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
The Automatic Level Control (ALC) system uses a compressor relay to switch 12 volts to the compressor motor. The electronic suspension control module (ESCM) receives inputs from the suspension position sensors and air pressure sensor to determine when to raise the rear of the vehicle by grounding the relay coil circuit, and monitoring to ensure it agrees with the command.