Thank you for all the information oceanbrave! I would up taking the rig to a local shop where they could run the codes. Looks like the compressor overheated and went bad. I found a second hand unit and installed that. The bags filled right up and all seemed well until I went to drive it home. I heard a load pop, almost like a gunshot, and the rear end dropped fast. I was only a couple of miles from home (if that) and kept on driving. By the time I was pulling into the driveway at home I heard a second pop and the rear was all the way down. I pulled the compressor fuse and drove it back to the shop the next day. Turn out that the cheap aftermarket bags I had just bought both popped from where the metal ring holds the top of the bags on. I went ahead and ordered some GM/Firestone bags and had them replaced. All seemed well until I got home again and the right side was considerably higher than the left side. I tried the extended ride height button and both sides were now level again. I drove around and the suspension eventually dropped to standard ride height, but the right side was still higher than the left. Back to the shop it is to see if a calibration would fix this. Apparently the module on the new to me compressor assembly is bad and won't communicate with a Tech 2. The module from the old compressor won't communicate either. So now I have a new module on order and hopefulle this nightmare will be over. Now I know why people just go with springs.

 

The "cheap" bags issue sounds plausible, however any grease on the air pipes might cause the same thing, they definitely run grease-free! (been there!)

Its unlikely that both modules have communications issues, it's more likely there's an issue with the serial comms such as a bad earth or broken connection. Are both modules the same GM Part Number? (out of interest what are they?)

To check the comms, unplug one of the ride-height sensors, eventually you should see a "Service Air Suspension", if not then it suggests the battery was reconnected without comms to the AS unit so the BCU thinks the AS is not there. If you've never seen a "Service Air Suspension" that in itself suggests there's a break in the comms circuit.

Hopefully your new module will do the trick, which means you've been very unlucky with the modules, however if that too doesn't work then it must be the wiring.

Oddly enough my module died with exactlty that problem, after repairing it I found there was a bad PCB track which could be a common problem but unlikely (my module was GM P/No: 10363984)

See JPGs for those who have never seen an AS module PCB before, the red wire fixed the broken track (trace) which was in fact the +12V power to the comms chip. Unfortunately this repair job is not easy as the module is potted in rubber and so probably not achievable at home.

 

Thank you for this information.