You've received some great advice above. You said that you scanned it and received some codes. Did you use a quality bi-directional scanner to read those codes? I ask because a quality bi-directional scanner will not only read codes, but it will also allow you to actually test the functionality of the various components of the active suspension system. This allows you to find the root cause of your issue quite easily.
I've had my truck with both passive (was that way when I bought it) and active (reverted back to OEM active) suspensions, and IMO, the OEM active suspension is far superior. I will say that it can be a matter of personal choice, as some folks on this Forum prefer an aftermarket Passive suspension.
I would start with checking out the compressor first. The compressor is easy to manually check out to see if it will run with a direct 12 volt feed. If you cannot get the compressor to start, it is easy to replace if you do any wrenching, and it will cost you about $300 for the compressor. Purchase with an OEM compressor or a Dorman compressor, only.
Once you get a working compressor, you can then check for air leaks in the tubing and the rear shock bladders, using the soapy water mixture in a spray bottle. These are usually the two most common points of failure on this active suspension. If the shocks require replacement, the GM OEM shocks are now guaranteed for life, and you should be able to purchase them for under $400 each, using RockAuto.com or GMPartsDirect.com, much cheaper than from the dealer. The rear shocks are easy to replace.
If you get to this point with a good compressor and rear shocks, and you still don't have a running active suspension system, get back to us, and we will walk you through the next steps for further diagnosis of other components of this active suspension system.