I posted earlier but can't seem to find it anywhere - so here goes again. I just bought an '04 Yukon XL. It seems to ride okay but has an error message on the DIC that the Autoride needs servicing. The shocks and air compressor look fine and all the fuses are good. However, I have not yet heard the air compressor start up and run. Any ideas on what could be wrong? I also noticed that the heater won't switch back and forth between the floor and mid outlets. It was stuck on the floor initially but now it stuck on the mid outlets. Do you think this is the flapper valve motor or the control itself? I also need to buy an owner's manual. Any ideas where I can get one? Thanks everyone. Wes