GM Service Manual Online
For 1990-2009 cars only
  1. Turn the ignition switch to the LOCK position.
  2. Turn the ignition switch to the RUN position in order to reset the ALC sensor timing circuit.
  3. Important: Support the rear wheels or support the rear lower control arms so that the vehicle is at the normal trim height.

  4. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
  5. Disconnect the link from the ALC sensor arm.
  6. Ensure that the ALC sensor wiring harness connectors are secure.
  7. Move the ALC sensor arm up. The compressor should turn on and the shock absorbers should start to inflate. Refer to Automatic Level Control System Operation Check if the compressor does not run.
  8. Move the ALC sensor arm down until the compressor stops.
  9. Move the ALC sensor arm below the position where the compressor stopped. The shock absorbers should deflate. Inspect for DTC's and/or replace the exhaust solenoid valve if the shock absorbers do not deflate.
  10. Connect the link to the ALC sensor arm.
  11. Lower the vehicle.