i have a 2001 GMC Yukon with autoride and when i took it in a couple of years ago, the mechanic notice that one of my rear shocks spring a leak in the shock. To my surprise, each shock cost 378.98 each! I asked them to give me a break because we are talking about close to 1200 in shocks alone and we haven't mention labor cost yet. This is one scenario, another could be a air line from the compressor to the individual shocks could be cut or damaged and leaking air, or on each sensor near the wheels, there is sensors with little arms attached to the position sensor that indicates to the compressor when to come on and not come on.
I hope this helps you. i have my own problem after I installed a 3" body lift, I don't hear the compressor come on any more and notice the rear shocks are deflated. they are usually hard and full of air. Someone told me that there is a height sensor in our vehicles, if you can help me locate where abouts mine is located I could solve my problem i think? Good luck!