Air ride will inflate but not deflate
 

Need your help Hummer people!

On our 2007 H2 SUV, the rear air compressor (air ride) will inflate to normal level. Or via the dash button will raise the vehicle another 2.5" to the top.

But the system will NOT deflate. No exhaust valve function.
Not with the dash button.
Not when it is supposed to automatically drop and level off vehicle once you hit 40MPH.

Took it to local GM dealer. They said there was a code C0711, but could not find out which part failed, without ripping the air ride into individual pieces and testing each one. And that would have cost a small fortune.

They suggest on the next step to replace the entire assembly #19303233, since not all components are available separately (like solenoid or ECU).
My concern is that this is a very expensive part in my country of Canada.

Any ideas of what the problem is? I can try dissecting the air ride, but need a starting point.
Please help!

Think posts are limited to a single PDF, the full description of the fault code C0711 is included here for reference, I'll add pics etc in the next post.

With my limited knowledge I'll try to help.

I assume the "Service Air Suspension" message hasn't appeared since you didn't mention it?

Firstly, access to a Tech2 would be an advantage, with this you can read rear leveling pressure and operate the exhaust valve plus many other things.

Possible faults as follows:-

1. Wiring.
2. Exhaust valve,
3. Pressure sensor.
4. ECU

The ECU circuit monitors the current drawn by the exhaust valve (around 375mA), although not shown on my wiring diagrams, specifically the exhaust valve is wired to ECU-24 (a kind of ground) and ECU-1 (12V control) Normally if the exhaust valve was "open circuit" you would get either C0660 or C0702 code being set.

There is a single exhaust valve which may be being energized but not operating i.e. either stuck, defective or blocked. I'm not sure it's serviceable and the one's I've seen were very corroded, but I've never tried to repair one myself.

It's a similar story with the pressure sensor, however the ECU cannot determine which sensor is not working i.e. ride-height sensors or air-pressure (around 21mA), in this case code C0696 is usually set. There has been another member who thinks he's had a faulty pressure sensor, but it was never 100% proven. The pressures are around 42psi (0,43V) at normal height rising to to 90psi (2.04V) when extended.

I would be tempted to disconnect the truck's battery, unplug the exhaust valve and try remotely powering it on, taking great care to support the truck should it work and the suspension collapses.

The fact that the ride-height will lift the extra 2" suggests that the air pressure is being correctly read by the ECU and, as you suggest, the exhaust side isn't working.

If manually operating the exhaust valve works then it's either a wiring fault or the ECU itself.

If you are working on the As Unit or ECU, disconnect the truck battery to avoid setting another DTC.

Here are a couple of pics.

https://cimg8.ibsrv.net/gimg/www.hum...fef68ddea5.jpg
https://cimg1.ibsrv.net/gimg/www.hum...1dffc73f78.jpg

Wiring diagram.

@oceanbrave

Wow! Thank you so much for the info.

As soon as I started the H2, I did get a "Service Air Suspension" message in the DIC.
I only got it once ever, and it never re-appeared even after other ignition cycles.

Unfortunately I do not have access to a Tech2. If I am going to keep this vehicle any longer, I may have to buy one. I see them for sale on eBay coming from China. Wonder if they are genuine Tech2 scanners, or some knock off?

As parts like the solenoid and ECU are not available separately, I though as the next step I would buy a used unit from a wrecker and see if that solves the issue (hopefully).
Then I could play with the old unit and see if I can rebuild it.

The new unit from GM is about $1900USD now with delivery. In Canada where I am, the list is $3700 (2960USD). Nuts!

Thanks again! Will update here with what I find.

The Chinese Tech2 are not genuine, however they function just the same but may not match the original build quality. A new Tech2 I believe is like $5k

You may find a replacement ECU, be aware the part number may have changed, eg my GM 10363984 is now 89060585.

The solenoid is actually forms part of the RH compressor, I've never heard of anyone repairing or replacing either. You may have some luck in finding one.

A 2nd hand unit with a matching ECU P/No would be a good investment, I did exactly the same as it worked out cheaper than buying an ECU.

Before I spent any money I'd definitely want to bottom-out the problem 1st, like I say just poke 2 long wires into the solenoid connector, connect 12V and see if it operates, it's resistance should be 19ohms. You could spend money and still have a problem, if say it's a ride-height sensor playing up.

As you can see my old one is very rusty, what it looks like inside I have no idea (taken today)

https://cimg9.ibsrv.net/gimg/www.hum...49a8028489.jpg
https://cimg3.ibsrv.net/gimg/www.hum...05a343cc35.jpg
https://cimg5.ibsrv.net/gimg/www.hum...5bef698e8b.jpg

Did you resolve your issue?

Hi @oceanbrave ,

For some reason, this forum does not email me alerts showing a new post on the thread. So sorry for my tardy reply.

This is what has transpired so far.

1. I took the vehicle into the local GM dealer. The tech was pretty good, and confirmed what I already knew. That the air ride will inflate, but will not deflate.
He suspects either the exhaust solenoid or the module are faulty. I suspect the same. He pulled the code C0711.
I asked him why he did not pinpoint the problem and his answer was that a) it would have cost me lot of $ in labor to drop the air compressor and start testing individual components, and b) that the suspect components are not available separately anymore. Only the entire air ride compressor assembly. So no point in testing further.

Not much else in the system that can be faulty, as far as I can tell, given the symptoms.
And since I plan on keeping the H2 for a while, even if the compressor is not the problem, it will be good to have a spare.

2. So I ordered it via Rock Auto in the USA. Best price I could find, and about half price of a local GM dealer.
However, a week later, they advised me that they can not obtain the part from GM. A week later!! What an utter waste of time.
I told them that various GM warehouses around the country showed stock. They said they can not pull stock from there.
Rock Auto must get it from a discounter somewhere, not directly from GM warehouses.
Anyway, they refunded me.

3. I then contacted Arnott, the suspension people, but they have discontinued their rebuilt version they used to sell at a discount.

4. I then ordered a brand new assembly #19303233 (the dual compressor version) from a local GM dealer. They are pulling it out of a GM USA warehouse and I am awaiting its arrival.
Should be here within a week.

I will report back once I have an idea of the repair (I plan to install it myself).

Question: is the air filter for the inlet/exhaust serviceable? It is at the end of a long tube, right behind the RL wheel inner fender. Between it and the inner bumper.
I can not see a way to open it and look inside to see how dirty it is.
A new one is expensive to replace for what it is. Any experience with it? I would hate to use a dirty filter on a new assembly.

PS> Can't tell what color your hood latches are on your avatar pic.
But I just bought 2 sets of chrome hood latch assemblies. Found this long-discontinued OEM stock on ebay.com (USA).
Someone had a pile of them. They have a few sets left when I last checked, in case you need some.

Cheers, same as yours, chrome. Could you re-post the hyperlink be good to get some:)

It seems mad, but I've never seen the other end's of the air-intake pipes. I was leaving it until did some work in that area.

Also I don't recall any pipes being connected to the exhaust valve, only the two air-intakes. I too replaced my AS Unit but with a 2nd hand one, I've just noticed they have different types of exhaust valves.

Old AS Unit

https://cimg2.ibsrv.net/gimg/www.hum...1d2c432440.jpg

Replacement AS Unit

https://cimg3.ibsrv.net/gimg/www.hum...3586d16d1e.jpg

Not sure if this means they are the same mountings i.e. interchangeable or serviceable.

One thing I do know is screws are hard to extract from the compressor diecast casing, the heads just twist off, otherwise I would try and remove mine, may still do, be interesting....