Suspension compressor issue

[Lonestar245]

2009 97x. My suspension air compressor doesn’t turn on. Note: the 2009 models DO NOT have the air inflator accessory with the small red indicator light in the cargo area. That said-
When I first started diagnosis I found the link on the passenger ride height sensor had broken. I made a new one out of a coat hanger wire. I measured carefully and it’s close enough that it should work. That didn’t fix the problem.
Next I pulled the dummy plug where the air inflator switch and light connect to the pump. I jumped the pins for the accessory inflator and the pump runs. It has the acc inflator output plugged, so the pump immediately builds pressure and slows due to high compression, so I believe the check valve is working.
Next I jumped the pins for the indicator light. I have been told one flash is catastrophic fault in the compressor, 2 flashes is drivers side height sensor bad and 3 flashes is passenger side height indicator is bad. I have tried every combination I can think of to get a signal off those pins and I get nothing. Rear end on bump stops, key on, engine started- nothing.
One side normal, other side low, key on, engine started, nothing. I’ve use a multimeter and got no reading from those pins in all sorts of configurations with ride heights and key on or engine started. I’m not sure where to go next. What am I missing?

 

[Mooseman]

You already know more than we do. I didn't even know about the diag feature on these with the light flashes.

That being said, this is such an expensive and problematic system that we typically suggest deleting it and replacing the bags with springs.

If you're really intent on keeping it, sounds like it's not getting the signal from the BCM to turn on. When the bags or valves go, the compressor will run but not raise the rear and eventually stops. Grab a copy of the repair manual (link in my signature) and check out the schematics for the wiring. Maybe it's just a break in a wire.

 

[Lonestar245]

I’m fairly certain the bags are ok, as when I tried to disconnect the lines at the pump, I got good compressed air hissing out of each before I fully disengaged the lines. For that reason I just tightened them back up. It’s possible they have a small leak, or the leak was somewhat sealed when the bags went almost fully down, as they roll over themselves. I have lifetime warranty on the bags from Arnott, so I’m less concerned about them. Just want to get the pump working again. I do carry some heavy loads sometimes, and tow a trailer. I love the air suspension for those reasons. Also, I have had to only replace the bags around 100k miles, so the cost of maintaining has been small.
Thanks for your response. Maybe someone else will have some further input.

 

[TJBaker57]

This offers a description of the system that may be helpful..

Suspension Control ( Automatic - Electronic ): Description and Operation — 2009 GMC Truck Envoy 4WD L6-4.2L Service Manual | Operation CHARM

Detailed repair manual for the 2009 GMC Truck Envoy 4WD L6-4.2L.

charm.li

 

[northcreek]

Since the compressor is a stand alone system I suspect that the internal electronics are the problem and that means a new compressor since there are no serviceable parts other than the check valve.
Make sure that your sensor repair is spot on and not causing it to go into lock mode because it thinks it is on uneven ground. For that matter, the sensor could be bad.