GM Service Manual Online
For 1990-2009 cars only

Rear Suspension Leveling Air Compressor

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

ALC Sensor

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

    • The Automatic Level Control Air Compressor.
    • The Exhaust Solenoid Valve.

The sensor circuitry provides a 25 second delay before either circuit can be completed to prevent falsely actuating the compressor or to prevent 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 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 to renew the 2.5 minute maximum run time. The sensor mounts on the rear shock and spare tire crossmember. The actuator arm of the sensor attaches to the rear differential case by a link.

Rear Leveling Shock Absorbers

The shock absorber is essentially 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. To maintain proper operation and to maintain reliability of the shock absorber a minimum residual air pressure of 55 kPa (8 psi) is maintained at all times by the air dryer.

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, locking the tubing in position. All tubing fittings are sealed with two O-rings.