Hello I checked the wiring nothing seems to be broken or shaped or pulled. So I started contemplating the ride height sensors the left one was reading at .35 the right one was reading at 0. 04. So I decided to check one of my old right side ride height sensors. We hooked up a scan tool this one was giving me 0.3 5 on the left hand side 1.41 on the right hand side. So with the scan too I also check them while the vehicle was running the left side coming in at 4.7 the right side showing 4.9. but still no luck with getting the height adjusted. Since the voltage is a little high on the right hand side after reading some it says I may have an issue with the electronic suspension control module. Not quite sure what all that means a little help in breaking that down would be deeply deeply appreciated
Thanks OB

 

If possible please quote all the DTC numbers you have, so, so important.

Strange your meter voltage readings were Left=0.3fV and Right=0.04V yet become 4.7V and 4.9V via the scan tool, they should be similar, say withing 20% as effectively the ECU is reading the same values, I'd be tempted to double check my data it's easy to get mislead.

If this the above is true, it could be a ground issue, things to check:-

1. G402 is an eyelet tag connecting the H2 chassis to the AS Unit chassis, measure the resistance between the two chassis it's vital this connection is good !!!
2. It's possible the "LO REF" is not connecting through to both sensors, H2 side is C451-R (2D Purple) to C451A-R (2D Yellow) which in turn connects to AS-ECU Pin-7

Effectively the Left/Right sensors are potentiometers physically connected to suspension, if the height is higher than "Calibration" the AS deflates the bags, if its lower than "Calibration" the AS inflates the bags. "Calibration" is the voltage reading taken by the ECU during a ride-height calibration, typically it's around 2.5V

To calibrate ride-height, the bags need to be deflated and the suspension mechanically set to the correct physical height (many posts on this) a ride height calibration is then performed.

Without trawling back through this post, I seem to recall the ride height was too high and not going down?

Suggest manually setting the rear suspension height to what seems right, then with the engine off read the height values via the Tech2, they should both be around 2.5V.

Can you deflate the suspension with the Tech2?

If not you could have a faulty exhaust valve, either electrically or blocked, again check the grounds.

Best I can offer without being there......

 

As I mentioned before I changed the ride height sensors with new ones. I bought two sets at two different times. Thinking the first pair may not have been compatible with the Hummer. Because of the readings my scanner was giving me the 0.35 on the left and 0.04 on the right. I got the same reading on both sets. So I changed the one on the right side back to the one that was on the H2 originally when I bought it. That one is reading 1.41. So I have on the left side a reading of 0.35 and on the right I have a reading of 1.41 on my scanner. That is with the ignition on. If start the H2 that's when the readings go up 4.7 on the left and 4.9 on right. So how do I manually lower the vehicle so I can check and see if I get the 2.5 reading you mentioned? Since my scanner won't lower it for me can you explain how to do it. I have searched and can't find a way to accomplish that.
In a previous post you mentioned the ECM may have issues as well. How do I check to find out if that may be a problem also? I pray to God all this makes sense!!
Thanks OB

 

As far as I'm aware, the Tech2 is the only tool that can calibrate ride-height, it's not to say yours can't as technology moves on, but that's the way it seems.

From the GM Manual the Air Suspension Depressurization procedure is as follows:-
To depressurize the Air Suspension System install the scan tool with key in the on position. Go to the special functions menu of the Air Suspension section and follow the on screen directions. The suspension will deflate the air springs until the suspension is on the jounce bumpers

From the GM manual for calibration to be achieved, both sensors must be in the range 2.06V to 2.88V

The "Jounce" tool CH-47816 are blocks that mount over the bump stops, they are expensive, hard to find and unnecessary, though personally I'd like a set.

Put the truck on level ground, jack the differential to achieve the correct trim height and follow the "Trim Height Calibration Procedure"

Re depressurization, it sounds like your truck lowers itself anyway (you quote 1.41V and 0.35V) so with the rear wheels on the ground and the trim-height set at 5.2" your diagnostic tool should read somewhere around 2.5V on each sensor, if not you may have an issue, otherwise you can try the trim height calibration below.

If depressurization is not achievable, it may possible to do it manually taking great care and is not recommended! Gently release the air bag lines, note there could be around 40psi in the each line, the rear needs supporting very safely incase of any sudden lost or change in suspension.



From the GM Manual Suspension Position Calibration is as follows:-

Tools Required
CH-47816 Suspension Position Calibration Blocks
Important: Before proceeding with the steps below, ensure:

• There are no stored diagnostic trouble codes stored in the ASCM.
• The vehicle is on level ground.
• There are no occupants in the vehicle.
• The tire pressures are at the recommended kPa/psi.
• All vehicle doors are closed.

1. Raise the vehicle on a hoist.
2. Install the CH-47816 on to the LR and RR jounce bumper mounting cups.
3. Lower the vehicle off the hoist.
4. Depressurize the air suspension system in order to allow the full rear weight of the vehicle to rest on the blocks and rear axle. Refer to Air Suspension Depressurization .
5. Turn ON the ignition, with the engine OFF.
6. Install a scan tool.
7. With the scan tool select Chassis.
8. Select Air Suspension.
9. Select Special Functions.
10. Select Trim Height Calibration and press the Enter key. The scan tool will flash Calibration In Progress, then display Calibration Complete.
11. Press the Exit key.
12. Pressurize the air suspension system until the rear weight of the vehicle is lifted of the blocks. Refer to Air Suspension Pressurization .
13. Remove the CH-47816 .
14. Ensure all vehicle doors are closed. Cycle the ignition switch OFF then start and run the engine for 2 minutes to allow the vehicle to level at the designed ride height.
15. After ensuring all vehicles doors are closed, use the scan tool to raise and lower the vehicle by commanding the extended ride height switch special function each time to verify the air suspension system is functioning properly.

You say,
"So I changed the one on the right side back to the one that was on the H2 originally when I bought it. That one is reading 1.41. So I have on the left side a reading of 0.35 and on the right I have a reading of 1.41 on my scanner."

this suggests your new sensors are perhaps the wrong ones?

All this info may seem "hyperbole" but the AS electronic control is a very sophisticated unit and its never going to work correctly by accident, all operating conditions need to be met, just like a password and login, one wrong character and access is denied, also DTC's are the key to everything !!

 

I had a set of the C-47816's when I had my 06, when I was having issues with the air suspension leveling, it was explained to me from a retired H2 mechanic when using the Tech 2 to do the calibration with the blocks when you put the unit into calibration mode the resistance was read when the axle was settled on the blocks and used to set "zero" position on the height calibration. This took into consideration the difference in resistance that the height sensors had as there was no real way of adjusting that value. Until I got the calibration blocks I was told to remove the 2 bump stops, cut a piece 2 pieces of 4x4 exactly the same height (unfortunately dont remember the measurement) and place them on the axle where the bump stops were. Use a large stainless screw clamp to hold them in place. When the calibration starts the system will inflate and deflate both air bags until the axle rests on the 4x4's and against the frame. It then would records the resistance of both sensors and that would become the "zero" position.

Stupidly, when I sold off my 06 for my 08 I sold off the blocks as another H2 owner really needed them more then me as my 08 unfortunately has coil springs. If someone has a factory tech manual we probably can figure what you would need to cut the 4x4's to in order to re-create the tool. For what its worth I have one of the most expensive Xtools on the market and it would not do the calibration correctly and always failed. The only thing that worked right was a GM Tech 2.

 

So after so much trial and mostly error with no success and my H2 still stuck at max ride height. I decided for the time being to convert to coil springs. This way I can at least drive it' until I can get the compressor and system checked out. I don't use my H2 for off roading it strictly a street driven ride. So far since the change over the H2 seems to ride pretty close to the same way it did before the change over. Thanks for all of your help with my problems. God bless all of you!