The automatic level control (ALC) system automatically adjusts the rear height of the vehicle in response to changes in vehicle loading.
The ALC system consists of the rear intergration control module (RIM), height sensor, an air compressor assembly, an ALC compressor relay, an intake hose and filter, an air tube, two rear shock absorber, and an accessory inflator switch. The air compressor assembly consists of an air compressor and an air dryer mounted on a bracket. The air compressor head is a replaceable part of the air compressor. The exhaust solenoid is a non-replaceable part of the air compressor head.
When a load is added to the vehicle, the vehicle body moves down causing the sensor actuating arm to rotate upward. (An arm movement of about 25 mm (1 in) amounts to a height change of about 12 mm (1/2 in) at the rear bumper.) The upward arm movement activates an internal timing circuit and, after an initial fixed delay of 17 to 27 seconds, the sensor provides a ground to complete the compressor relay circuit. The 12V (+) circuit to the compressor is then complete and the compressor runs, sending pressurized air to the struts through the air tubes.
As the struts inflate, the vehicle body moves upward rotating the actuating arm towards its original position. Once the body reaches its original height, +/- 25 mm (+/- 1 in), the sensor opens the compressor relay circuit, and the compressor is turned off.
SO what all this means is that the sensor acutacting arm has come loose, or the sensor has gone bad. Unfortunatelly, there are a few proceduers that you can perform, but they all require the Tech 2. Check to see First if the sensor actuating arm is still attached to the drivers side controll arm