Well, a couple of questions. Is there a way to check the compressor to see if it's working properly. Maybe sit on the rear end? Is it operable even if the car is sitting? My Deville seems to be "low" in the rear. Don't know if is a bad compressor, leaking shock(s), or both. If it is a leaking shock, I don't want the compressor to run all the time. I assume I could hear it when the car is off. ? I wasn't sure if there is a code for the leveling system or not. When I jacked the right rear of the car up(Flat tire post) it was hissing as I was jacking. Is that normal? Thanks all for your help! V.