wrote:
> On Saturday, January 20, 2018 at 1:36:08 PM UTC-5,
> wrote:
>> My wife has a 2006 GMC Envoy, {Denali}. It has the air suspension
>> in the rear. 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 attention to what it
>> could have been. It almost seemed like someone had bumped 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 end 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 wife'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 obvious 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 enough 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 normal 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 "bumping" 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 this friggin car is}. Is there however a procedure that
>> you may know of where 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 really 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 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

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.