The air dryer is equipped with valving that maintains a residual pressure of 48 to 97 kPa (7 to 14 psi) in the shock absorbers to improve ride characteristics during light load conditions. Additionally, shock absorber air sleeve life is improved when the ALC system maintains residual air pressure. The following steps must be followed to perform the Residual Air Pressure Check properly.

Important: The vehicle must be raised on a drive-on lift. The full vehicle weight must be on the rear tires.

1. Raise the vehicle. Refer to Lifting and Jacking the Vehicle .
2. Disconnect the air tube from the air dryer.
3. Connect the J 22124-91 pressure gage adapter to the air dryer.
4. Connect the J 22124-B pressure gage to the J 22124-91 pressure gage adapter. Open the J 22124-B pressure gage toggle valve.
5. Disconnect the air tube from one shock absorber.
6. Connect the adapter tube supplied with the J 22124-B pressure gage to the shock absorber and to the J 22124-B pressure gage.
7. Disconnect the link from the height sensor and move the arm up. The air compressor should operate, inflating one shock absorber.
8. Move the arm down. The air compressor should stop and air should be escaping. Allow the rear of the vehicle to go down as far as possible.
9. Connect the link to the height sensor.
10. Read the pressure gage.

If the pressure gage reads less than 48 kPa (7 psi), replace the air dryer. Refer to Automatic Level Control Air Dryer Replacement .

11. Disconnect the J 22124-B pressure gage and J 22124-91 pressure gage adapter from the air dryer and shock absorber.
12. Connect the air tube to the air dryer and the shock absorber.
13. Lower the vehicle. Refer to Lifting and Jacking the Vehicle .