Strange rear air shock behavior.

[Geotrash]

No sooner did I replace the rear air shocks on my 2012 Denali, and the rear air shocks on my 2007 Denali started acting up.

Specifically, when hauling a trailer (400 lb tongue weight), the suspension airs up just fine when I connect the trailer, and will kick on as I drive to keep the suspension level, at least for a while. At some point, that stops happening and the rear end begins to sag though it’s difficult to tell from the driver seat. I only discover that the suspension is no longer airing up when we stop at a rest area, or to get gas. Then, when I start the engine again, the compressor kicks on like normal and we drive away fully level, until at some point it begins to sag again.

I’ve checked the air bags and all connections with soapy water, and can detect no leaks. When I leave the trailer hooked up with the suspension level and the ignition off, it takes about 20 minutes for me to detect that the suspension is starting to sag, so there’s likely a very small leak, but both air bags seem to stay pressured up pretty well.

Anyone know what would cause the compressor to stop kicking on while driving? One hypothesis is that the compressor is having to kick on often enough to overheat it. But not so much for it to fail completely. No service suspension messages and no errors detectable with the tech2.

Thanks for any and all help.


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[kses123]

The pump could be leaking or the solenoid could be stuck. The pump will stop running if it has been running for an extended period of time. I don't think it cares about cycling too often, just running for too long at once. Is it the original pump or a replacement?

 

[Doubeleive]

mine was doing something similar, it would air up and then throughout a drive it would loose air, if you cycled the key it would air up again and then again loose air or if you checked it in the morning before starting it up the bladders would be pretty much flat, turned out the pump was leaking air out of the intake tube found the leak with soap/water, I would get a slow bubble out of the line. So if the shocks are not leaking check your pump for leaks also

 

[Geotrash]

The pump could be leaking or the solenoid could be stuck. The pump will stop running if it has been running for an extended period of time. I don't think it cares about cycling too often, just running for too long at once. Is it the original pump or a replacement?

Thanks for your thoughts. I don’t know the answer. I bought the truck with 196k on it so my guess is probably not original but I don’t know how old it is. The truck was extremely well maintained though, and was a one owner rig from Arizona.


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[Geotrash]

mine was doing something similar, it would air up and then throughout a drive it would loose air, if you cycled the key it would air up again and then again loose air or if you checked it in the morning before starting it up the bladders would be pretty much flat, turned out the pump was leaking air out of the intake tube found the leak with soap/water, I would get a slow bubble out of the line. So if the shocks are not leaking check your pump for leaks also

That’s a great lead, thank you. I’ll look at the pump itself next.


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[Geotrash]

Another small update: I hooked up the Tech2 today and went into Suspension Control Module -> Compressor Test and commanded the compressor to come on. No response, but commanding the purge valve on worked - I could hear it release air. I exited out of the system, unhooked the Tech2 and cycled the ignition. The compressor didn't come on for a self test. So I took a short drive, came back and cycled the ignition again. Still no self test. So I climbed on the back of the truck hoping my weight would trigger the compressor, which it did. I'm no further to answers, but wanted to at least share an update. Also, all sensors showed normal voltage on the Tech2 for the suspension system.

Also, I didn't find any leaks at the compressor with soapy water but I did check the bags again and both are leaking slightly at the edge of the boot above the band clamp.

 

[Doubeleive]

Another small update: I hooked up the Tech2 today and went into Suspension Control Module -> Compressor Test and commanded the compressor to come on. No response, but commanding the purge valve on worked - I could hear it release air. I exited out of the system, unhooked the Tech2 and cycled the ignition. The compressor didn't come on for a self test. So I took a short drive, came back and cycled the ignition again. Still no self test. So I climbed on the back of the truck hoping my weight would trigger the compressor, which it did. I'm no further to answers, but wanted to at least share an update. Also, all sensors showed normal voltage on the Tech2 for the suspension system.

Also, I didn't find any leaks at the compressor with soapy water but I did check the bags again and both are leaking slightly at the edge of the boot above the band clamp.

if it was me I would replace both the rear shocks with the arnott's and a dorman pump, then you have a lifetime warranty, the arnott's are about 1/2 the price of oem. just be sure to get everything from a authorized dealer to retain the warranty. rockauto sells the arnott's and o'reilly's has the pump. that's what I did I originally went with the arnott pump also but 2 of them failed on me, the shocks have been fine and the dorman pump has been fine

 

[Geotrash]

if it was me I would replace both the rear shocks with the arnott's and a dorman pump, then you have a lifetime warranty, the arnott's are about 1/2 the price of oem. just be sure to get everything from a authorized dealer to retain the warranty. rockauto sells the arnott's and o'reilly's has the pump. that's what I did I originally went with the arnott pump also but 2 of them failed on me, the shocks have been fine and the dorman pump has been fine

That's probably what I'll do. But I'm a little concerned about the Arnott shocks since they only replace the boots and don't do anything with the internals when they "rebuild" them. The OEMs are only $250 each. For $100 extra for a set over the Arnott's I'd rather have new. Chances are I'll never wear them out.

 

[Doubeleive]

That's probably what I'll do. But I'm a little concerned about the Arnott shocks since they only replace the boots and don't do anything with the internals when they "rebuild" them. The OEMs are only $250 each. For $100 extra for a set over the Arnott's I'd rather have new. Chances are I'll never wear them out.

you might be getting that from old info, the arnott's I received are partially remaned oem but the design is completely different than the oem shock they made a change in them at some point had to be over 3 years ago when I bought mine

 

[Geotrash]

That's helpful info, thank you. I do like the lifetime warranty idea.

 

[Geotrash]

I ended up ordering new OEM air shocks from rockauto just like I did for Denali #1 last month. I also swapped out the compressor with a new Dorman unit. Got it all installed this evening in a couple of hours and everything seems to be working great. Air bags are plumped up and holding air. I’ll be hooking up the camper for the weekend tomorrow so I’ll see how she does on the trip and report back.


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[Geotrash]

Confirmed that the problem is solved. No sagging after a couple of hours on the road tonight.


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[Rocket Man]

Confirmed that the problem is solved. No sagging after a couple of hours on the road tonight.


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Awesome, glad you got it fixed. So many people think these systems are complicated or too expensive to repair and get rid of them but it’s nice to have the self leveling when towing or hauling a heavy load.

 

[Geotrash]

Awesome, glad you got it fixed. So many people think these systems are complicated or too expensive to repair and get rid of them but it’s nice to have the self leveling when towing or hauling a heavy load.

I agree. It’s a great system and awesome for towing. Easy to work on as well.


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[iamdub]

Awesome, glad you got it fixed. So many people think these systems are complicated or too expensive to repair and get rid of them but it’s nice to have the self leveling when towing or hauling a heavy load.

And there are others that are forced to get rid of the ALC shocks in the pursuit of moar lowz but still realize the value of it and try to Frankenstein alternate solutions. Those people are stubborn and gluttonous idiots.


BTW, I'm still not quite finished experimenting with mine yet.

 

[Rocket Man]

And there are others that are forced to get rid of the ALC shocks in the pursuit of moar lowz but still realize the value of it and try to Frankenstein alternate solutions. Those people are stubborn and gluttonous idiots.


BTW, I'm still not quite finished experimenting with mine yet.

 

[Geotrash]

One more thing I noticed about the new rear suspension components, is that they don’t sag even after the truck has been sitting for a couple of hours with a trailer attached. It’s a good sign that the system is on the way out, in hindsight, when the rear end squats after a little while due to slow leaks. My guess is that those leaks compound while the suspension is in motion during travel, and eventually overwhelm the compressor.


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[Trailblazzin]

One more thing I noticed about the new rear suspension components, is that they don’t sag even after the truck has been sitting for a couple of hours with a trailer attached. It’s a good sign that the system is on the way out, in hindsight, when the rear end squats after a little while due to slow leaks. My guess is that those leaks compound while the suspension is in motion during travel, and eventually overwhelm the compressor.


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Did you try to command the new pump on with the tech2? I had a faulty ride height sensor in the rear, replaced and all senors seem to be within voltage, but i can’t make the pump come on with the trch2, but the pump will run with key on and air up as needed. The release solenoid I can hear click but don’t hear any air escaping. Is that normal?

 

[Geotrash]

Did you try to command the new pump on with the tech2? I had a faulty ride height sensor in the rear, replaced and all senors seem to be within voltage, but i can’t make the pump come on with the trch2, but the pump will run with key on and air up as needed. The release solenoid I can hear click but don’t hear any air escaping. Is that normal?

I wasn't able to command the old pump to come on with the Tech2, but haven't tried it with the new one yet. If I get a moment today, I will go out and try it again now that the new pump is installed and working great.

Just curious - how did you determine one of your ride height sensors was bad? Was one of them outside of the normal voltage range?

 

[kses123]

I think you'll be happy that you got OEM components over the aftermarket "rebuilt" units. The extra money is worth the peace of mind in my opinion.