2006 GMC Envoy, (denali) rear air suspension problem

My wife has a 2006 GMC Envoy, . It has the air suspension in the re ar. You can hear the compressor come on almost every time you start the car
. For the last few months we have been noticing that after turning off the car for instance and if you're just sitting in it for a period of time you can feel every so often a minor "thump" sound. We never really paid much at tention to what it could have been. It almost seemed like someone had bumpe d us very slightly from the rear but it was so minor it was insignificant. These little aberrations were spaced apart sometimes by 10 minutes or more and like I mentioned seemingly insignificant.
Last week I got home after my wife did and noticed the rear of her car was very low to the ground. The next morning she started the car and the rear e nd pumped up to where it should be. I'm sorry to say that I can't tell you if this has been happening for any particular period of time. This is my wi fe's car and she would usually never notice something like this. It was OK for a week or so and then yesterday I borrowed it to do a couple of errands . I made my first two stops did my errands and when I got in the third time I neglected to check the height. As soon as I took off though it was obvio us that it was dragging ass. Every bump felt like a mountain and it was not pumping back up. I stopped, shut the car off and looked at it and sure eno ugh it was very low. My errand took about 5 minutes and when I started it u p again after about 15 seconds the compressor came on and pumped it up to w hat looked like a correct height to me. And the 6 mile ride home was a norm al one. We just checked it this morning and it's down again. We started it up and it pumped back up to normal height. I've since realized that the "b umping" feeling that we first experienced last Spring was probably the rear end very slowly losing air, for what ever reason.
So I'm sure that this is not a simple system to troubleshoot, (nothing on t his friggin car is}. Is there however a procedure that you may know of wher e I could try to do this.The problem seems sporadic though so I wonder if a ny diagnostics would even be valid? The biggest problem is that I don't rea lly understand the system so at this point I can't do too much. And all the dealer says is "this is going to be expensive". Thanks for any help and ad vice. Lenny
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There's a leak.
You can find the leak by putting the thing up on the rack and using a piece of fuel hose as a stethoscope and moving it around. When you find the leak, it will be pretty evident.
The leak is not going to be a subtle and minor thing. You only notice it when it's so bad that the compressor can't keep up, but it's always leaking throughout.
It likely WILL be expensive because likely the leak is in the actuators, and it won't be fun to remove them. It may be possible to rebuild them yourself rather than replacing them, though.
You don't need to understand the system too well to fix this. There is a lot of very sophisticated stuff going on inside the control box, but none of that is broken so don't worry about it (unless you like feedback control theory as a hobby). From your perspective, the computer opens valves that force air into actuators and in one or more places the air is leaking out of the sealed system. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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On Saturday, January 20, 2018 at 1:36:08 PM UTC-5, snipped-for-privacy@gmail.com w rote:

rear. You can hear the compressor come on almost every time you start the c ar. For the last few months we have been noticing that after turning off th e car for instance and if you're just sitting in it for a period of time yo u can feel every so often a minor "thump" sound. We never really paid much attention to what it could have been. It almost seemed like someone had bum ped us very slightly from the rear but it was so minor it was insignificant . These little aberrations were spaced apart sometimes by 10 minutes or mor e and like I mentioned seemingly insignificant.

s very low to the ground. The next morning she started the car and the rear end pumped up to where it should be. I'm sorry to say that I can't tell yo u if this has been happening for any particular period of time. This is my wife's car and she would usually never notice something like this. It was O K for a week or so and then yesterday I borrowed it to do a couple of erran ds. I made my first two stops did my errands and when I got in the third ti me I neglected to check the height. As soon as I took off though it was obv ious that it was dragging ass. Every bump felt like a mountain and it was n ot pumping back up. I stopped, shut the car off and looked at it and sure e nough it was very low. My errand took about 5 minutes and when I started it up again after about 15 seconds the compressor came on and pumped it up to what looked like a correct height to me. And the 6 mile ride home was a no rmal one. We just checked it this morning and it's down again. We started i t up and it pumped back up to normal height. I've since realized that the "bumping" feeling that we first experienced last Spring was probably the re ar end very slowly losing air, for what ever reason.

this friggin car is}. Is there however a procedure that you may know of wh ere I could try to do this.The problem seems sporadic though so I wonder if any diagnostics would even be valid? The biggest problem is that I don't r eally understand the system so at this point I can't do too much. And all t he dealer says is "this is going to be expensive". Thanks for any help and advice. Lenny
I really like the idea of the hose as a stethoscope. Can you please tell me what is an actuator? Do you know if there are any pictures of this system and these actuators anywhere that I could look at? Lenny
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snipped-for-privacy@gmail.com wrote:

Go to 2carpros.com Ask the question there and fill in as much info as you have here. There people can add pictures and instructions on how to test the system. It isn't really that hard, it's basically air shocks with ride height sensors that add/subtract air based on where the sensors set. In your case it's leaking down while setting so it isn't the sensors. It is a leak between the compressors and the rear air bags.
--
Steve W.

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