GM Service Manual Online
For 1990-2009 cars only

Rear Suspension Leveling Air Compressor

The compressor is a positive displacement rocking piston air pump that is powered by a 12-volt direct current permanent magnet motor. The compressor head casting contains the piston intake valves and the piston exhaust valves. The compressor is mounted to the right front of the body by a bracket.

ALC Sensor

The ALC sensor is an electronic device. The following items are controlled by the ALC sensor:

    • The rear suspension leveling air compressor
    • The exhaust solenoid valve
    • The fault indicator
    • The serial communication

The sensor circuitry provides a 25 second delay before either circuit can be completed. This prevents falsely actuating the compressor or prevents falsely actuating the solenoid valve circuits during normal ride motions.

The sensor also limits the compressor run time or the solenoid valve energized time to a maximum of 2.5 minutes. This time limit function is necessary in order to prevent continuous compressor operation in the case of a severe system leak, or in the case of a continuous exhaust valve operation. Turning the ignition off and on resets the electronic timer in order to renew the 2.5 minute maximum run time. The sensor mounts on the rear axle cradle. The actuator arm of the sensor attaches to the right rear lower control arm by a link.

Rear Leveling Shock Absorbers

The shock absorber is a conventional shock absorber enclosed in an air chamber. The shock absorbers are constructed with a rubber-like sleeve attached to the dust tube and attached to the shock reservoir. This makes a flexible chamber which extends the shock when the air pressure in the chamber is increased. The weight of the vehicle collapses the shock absorber when the air pressure is reduced. A minimum residual air pressure of 55 kPa (8 psi) is maintained at all times by the air dryer in order to maintain proper operation and reliability of the shock absorber.

Tubing and Fittings

The snap-on connectors attach the tubing to the rear shock absorbers. The connector housings contain retainer clips. When a tubing is attached to a shock fitting, the retainer clip snaps into a groove in the shock fitting. This locks the tubing in position. All tubing fittings are sealed with two O-rings.

Air Compressor Filter

The air enters the ALC system through the filter mounted to the air compressor bracket. The filter housing contains a foam filter. The foam filter prevents contaminants from entering the ALC system.