So, this is another "air compressor wont shut off issue", but I'm wondering if it's a little different than the other posts I've read here. Before I explain why I think this might be different, let me give some background. I have a 2004 H2 with the adventure package air pump accessory in the cargo area as well as air suspension. About a year ago it had the sagging rear end issue and I replaced both air springs which fixed the problem. The air suspension seems to work perfectly ( no sagging, no apparent leaks, no "service air suspension" messages), except the compressor will not shut off when ignition is shut off. I have to remove the fuse. So here is where I think this may be different than other posts.... I believe it's only one of the compressors that is running. I believe it's the one for the cargo area inflator and not the air suspension. I read in another post here that the adventure package comes with a dual stage compressor, and I'm not sure what that means. Two compressors? One compressor with two speeds? One compressor with two valves? Anyway, I know that when the truck is off and the compressor is running, I get compressed air out of the cargo area valve. If I turn the truck on I can hear what sounds like a second compressor turn on (air suspension I assume) and then shut off all while the cargo area compressor keeps running. Has anyone run into this version of the problem? If so, was the fix still changing out the relay near the front wheel well? Is there a second relay controlling a second compressor somewhere?

 

GM made a change to the compressors to a dual compressor setup but it was nothing to do with the adventure package nor was it that one is used for the rear accessory inflator and the other for the suspension. It was just a better overall design from what I read. On the older single compressor setups there is also a software update that corrects some issues but you have to have a dealer install that. That update has a warning about not installing it on a vehicle that has had the single compressor replaced with the dual style compressor. I forget what year that they implemented the change to the dual compressor style.

My 2003 has the older single compressor setup, air ride, and the accessory inflator. If yours has the newer revised dual compressor they are both used at the same time when in use. There was never a configuration where one was just for the accessory and the other just for the suspension. When the suspension needs air they both run, same as with the accessory air switch in the back.

As far as what is causing the problem you are having, I'm not totally sure. I'd almost want to guess that the computer that controls the compressors might be failing. There is no valid time that the switch in the rear should be able to turn the compressors on if the engine is not running and the shifter in park according the manual. "The engine must be running and the gearshift lever must be in PARK (P) for the inflator to operate."

 

Thanks MixMan. Your response helps me better understand how these double compressors are suppose to work. It's clear though that for some reason, one of my compressors is not responding to the same signals that the second compressor is receiving. I will try and look up a diagram of the double compressor system and see what kind of components it has. Maybe you're right and there is a some kind of computer or circuit board that receives signals from the hight/pressure sensors and issues signals to the compressors. Maybe it's faulty. If anyone else out there has any insight on the cause, I'd love to hear it.

Thanks again Mixman.