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Gm Tech (Cam)
Gm Tech (Cam), GMC Mechanic
Category: GMC
Satisfied Customers: 1667
Experience:  GM Grand Master Technician 2007. 14 year experience.
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2005 Envoy Denali. Replaced Air Suspension Compressor with

Customer Question

2005 Envoy Denali. Replaced Air Suspension Compressor with identical part. Compressor turns on with manual inflation switch but does not pump up airbags when starting the vehicle. Power supply is good, ground is good, all fuses checked and are good. Doesn't seem to be sending any voltage to either leveling sensors. What am I missing?
Submitted: 9 months ago.
Category: GMC
Expert:  Christopher Trevino replied 9 months ago.

Hello, I saw your question going unanswered and I wanted to assist you here. I've fixed a similar problem on a Cadillac Escallade, These systems tend to be similar, I wanted to see if I could help you here. Is your Denali giving you a "SERVICE RIDE CONTROL" or "SERVICE AIR RIDE" on the DIC display in the instrument cluster? If so you will need to use a certain type of scantool that will communicate with this ESC module to see what codes are active or stored in the module. The module closes the ground for the ALC relay circuit to power the compressor. If you can post the codes here , I can continue to assist you here. Thank you,

Customer: replied 9 months ago.
No error messages on instrument panel regarding air ride system. I do have a "service airbag" message but I'm pretty sure it's referring to the actual SRS because the "bubble gum guy" light is on as well. Also, the air compressor manual switch has a light on it. If there are malfunction codes it's supposed to flash with 1 of 3 sequences depending on the code. It doesn't flash at all, so no codes. I just pulled the automatic sensor plugs and tested them. I'm getting 3 ohms of resistance coming in (sent from compressor) and nothing coming out, which to me would indicate the signal from the compressor is good. I had the same problem with the previous compressor which I thought the problem was but I'm having the same issue even after I replaced it with a new one. Ironically, from time to time that compressor would kick on and fill the airbags. After time, the truck would start to sag and the compressor would not be triggered. It's an intermittent problem. I removed and cleaned the ground to the vehicle frame because I suspected that could be the issue but not to my surprise it wasn't. I'm stumped.
Expert:  Christopher Trevino replied 9 months ago.

Ok got it , thank you for the details. take a look at the wiring diagrams I have posted here, If you can post the diagrams you have I'll compare the two. Here's what I got for an 04 Escallade ESV. If I cant help you here I'll re-submit your question so hopefully a GMC Tech can further assist you. I Just want to make sure you get taken care of first and foremost!

Customer: replied 9 months ago.
The wiring schematic for my 05 envoy is way different and much simpler. I've attached it.
Expert:  Christopher Trevino replied 9 months ago.

I got it , thank you. Have you tested resistance from the other side of the plugs from the level sensors. not the harness to the module , but the sensors themselves? I just wonder if they are open or shorted, 0.2 ohms would be shorted and OFL would be electrically open as I'm sure you already understand. Also, if you have the electrical pin breakdown for the compressor would help. If the exhaust solenoid fails , it shuts down the compressor as well. However manually closing the switch closes the ground to power up the compressor. You are pretty much doing what the module should be doing but it cant because its not getting the correct inputs from either the steering sensors (if applicable ), level sensors, exhaust solenoid ect. I"d like to see what codes are present , The SRS codes may also interfere with this operation. I would start ohm testig the level sensors and any component possible related to the compressor for opens or shorts, then if still inconclusive , scan all the codes present on the truck to see what the module is seeing and that should guide you in the right direction.

Customer: replied 9 months ago.
In the schematic I sent you, there are 2 plugs. 1 has 8 pins labeled A-H and the other has 3 A-C. I haven't tested the resistance on the sensors themselves because if they were bad I'm supposed to get either the service air ride message and/or the blinking light on the manual air switch. Also, if one goes bad the vehicle reads off the working sensor for both sides, but then again, it's supposed to show a fault that a sensor is not relaying feedback. I've test the exhaust valve, it works. The end of the exhaust line is located next to the manual air switch and I can here it exhaust when I manually turn the switch off and on. What I'm trying now is, I jacked up the body to what is called "D Height" and am resetting the ecu to try to get it to recalibrate or learn the height to see if that works. Being that the vehicle is sagging very low I'm hoping that once I lower it, the recalibration will trigger the compressor and fill the bags.
Expert:  Christopher Trevino replied 9 months ago.

That sounds like a plan, next chance you get , with all the connectors plugged together , back probe points H and D you should get 12volts. and with the key in the run position, points G and D you should get 12 volts. By the way, you don't happen to be in any freezing weather conditions? Freezing temps seem to lock the compressors up. Usually below (25deg). Let me know how it goes, ill check back tomorrow. Best of luck!