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Premium Member
07 Black TBSS
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6,248 Posts
Discussion Starter #1
Hey guys and gals,

My sister drives a 2005 or 2006 GMC Envoy Denali. She parks on a driveway, which is slanted, but nothing terribly bad. She is having a problem with her rear bags completely deflating over night. This problem has started occurring more frequently. Sometimes, it takes a while before the bags will inflate and overall, it is an alarming problem - especially since she drives with 3 kids in the car nearly every day.

We have thought about replacing the bags, but I'm not convinced that the bags are the problem. Maybe 70K miles on the truck. The sensor bolts are tight and all else seems fine, aside from the fact that the bags deflate over night nearly every night!

Has anyone had similar problems? What did you do to fix? Any recommendations?

Thank you in advance!
JD
 

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Premium Member
07 Black TBSS
Joined
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6,248 Posts
Discussion Starter #2
Anything guys? I'm thinking maybe the rear level sensor? How much are these to replace.
 

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Premium Member
07 Black TBSS
Joined
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6,248 Posts
Discussion Starter #3
How about the compressor check valve? How much for a new one?

I found this:

The air bag going down is a release of pressure due to a faulty check valve possibly,a faulty reading height sensor,or a leaking bag.To determine which of these problems you have one will need to test & verify the system components.I suggest having a qualified technician scan date for the system,which may help find the fault.

Here is a system description of operation.





The air suspension compressor assembly houses the DC motor/air compressor, the air suspension control module (ASCM), an exhaust valve solenoid, and two air spring isolation valve solenoids. The ASCM sends a voltage signal to each height sensor and measures the inductance of the return signal to determine if one or both air springs need to be inflated or deflated. Before the compressor starts, the exhaust valve will be activated to provide compressor head relief. After this, the compressor relay will activate to start the compressor. When the trim height is achieved the relay will be deactivated. To prevent the compressor from overheating, the compressor operates on a duty cycle. If the compressor is requested to operate continually, the compressor duty cycle is limited to 300 seconds at maximum output for the first cycle. After this time, the compressor is automatically switched off for at least 92 seconds. Once this time has been met, the compressor will activate for 16 seconds and deactivate for 92 seconds. This 16 second/92 second duty cycle will continue until the compressor can remain off for more than 92 seconds. During this time, the indicator LED on the air inflator switch will be quickly flashing at a constant rate.

The air suspension compressor assembly has three different operating modes. Single Value Mode inflates and deflates the two air springs independently. This is the normal operating mode of the system. The system will enter Mean Value Mode when the sensor output indicates the difference between the D-height on each side is greater than 15.5 mm. In Mean Value Mode, the ASCM will average the signals from each height sensor to maintain an average trim height. If the measurement differential between the two D-heights reaches approximately 54 mm, the system will enter Lock Mode and no leveling will take place. This is to compensate for uneven loading of the vehicle or the vehicle being parked on an uneven surface. The air suspension compressor assembly also has a wheel change (jack) control that prevents the air springs from deflating completely. If the ASCM detects that one or both of the rear wheels has a D-height measurement of more than 235 mm, the system will enter Lock Mode and will suspend all leveling functions until the suspension is moved toward the frame.

The air suspension compressor assembly has the ability to detect faults and indicate the appropriate fault code via a blink code on the inflator switch LED. The air suspension compressor assembly will indicate the code when the condition that caused the code is current. In some instances the air suspension compressor assembly may set a flag that requires the ASCM to be reset. The ASCM will reset on its own after the ignition has been turned off for more than 2 1/2 hours or if the air suspension fuse has been removed with the ignition key turned off.



Read more: GMC Questions - 2003 Envoy right rear air bag goes down but not consistanly - JustAnswer http://www.justanswer.com/gmc/3l0bn...-goes-down-not-consistanly.html#ixzz1BntcFYpa
 

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Administrator
Trailblazer SS
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30,400 Posts
Do yourself a favor do the spring/shock combo i have here with the belltech 1 inch spacer. will ride better than what you have now and sit about the same height.
 

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Registered
2008 TbSs
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791 Posts
I agree with NORCAL. Have the same set up and you will be happy..:yay2:
 
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