2018 Tahoe Premium Magnetic Ride is Stiff

[Mich_tahoe]

My Tahoe has the Z95 magnetic leveling suspension and the rear shocks became very stiff, like I had no shocks at all. When I looked at them the air bags are inflated. I took it to my mechanic who has an OBDII scanner and it shows the shocks are connected. We both shook the Tahoe and you can see the shocks responding on the scanner. There are no codes. The shocks do not show signs of leaking but my mechanic pushed his finger up under the one shcks air bag and he got this sliver grease like substance on his finger. I checked all the fuses and relay and they checked out. What is not happening is the air compressor is not turning on when you start the car. To be honest I never heard it come on in the past. I removed the replay and used a jumper and the compressor came on so it works. We turned the Tahoe off completely and replaced the relay and then removed the air lines from the 2 rear shocks and heard air coming out and the air bags decompressed. We reattached the air lines then started the Tahoe and in about 8 second the compressor came on for several second and inflated the bags, shocks still stiff.


At this point the compressor works, it appears the relay is working because the compressor came on after starting and the air bags filled up, plus the shocks are communicating as we see them on the scanner. So what needs to be resolved is why the compressor does not come on when the air bags are inflated (maybe this is normal?) and what is causing the shocks to stay stiff and what is this silver grease under the air bag. Any and all assistance on this is very much appreciated. BTW My mechanic is leaning towards replacing the shocks.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

When you perform a cold start the truck, there is a self-check and level reset procedure that is supposed to take place, and it appears that it is not happening on your truck. The self-check process involves a release of air from the shocks through a valve within the air compressor assembly, and then the compressor comes on and re-inflates the shocks to a level truck position. That is when you should hear the compressor come on for 4-6 seconds shortly after the cold start.

IMO, that self-check and level reset procedure is not taking place properly on your truck. If your Mechanic has a quality bi-directional scanner, he should be able to manually perform this procedure using the scanner and observe what is taking place within the compressor and the Suspension Control Module. He should also be able to see what the air pressure is in the shocks, and I believe that it should be in the neighborhood of 20 psi for an empty truck.

From what you describe, I don't believe that the source of your issue is the shocks themselves. I believe that the air bleed valve in your compressor assembly is more likely the source of your issue, or the Suspension Control Module itself. A quality bi-directional scanner should be able to help you zero in on the source of your issue.

 

[GMCChevy]

That it ran on its own when you release the air seems to indicate that it's sort of working properly and holding air. There's a ride height sensor back there, maybe it's not adjusted right or not working so it thinks there's a load and going to full pressure because nothing is stopping it. I'm not sure what those compressors do at full pressure but that might be why it doesn't run.
Did you try releasing the air with the Tahoe sitting on its wheels to see if it's normal ride height or not?

On my 2017 it works like any other GM has for decades with the self leveling- it runs briefly after the ignition is turned on and then when the load changes either with heavy cargo or a bunch of people. If it doesn't run at all obviously something is wrong and if it runs pretty regularely with no load usually either it has a leak or its compensating for worn out springs.

 

[Mich_tahoe]

Thanks for all your replies.

My mehanic is overloaded with work so I will get with him this week to go over the above suggestions. In the menatime I did lower the Tahoe onto the ground and disconnected the air lines. Not much air came out and the shocks did not appear to change in height, still look fully extended. Reconnected the air hose and started the Tahoe and after a few seconds the compressor came on for about 5 seconds and stopped.

If just a small amount of air comes out and the shocks are fully extended what is keeping them extended? Is there more air stored in the shocks?

 

[SpareParts]

I think if the shock is fully extended it is bad. There is nothing i know of that would cause it to stay fully extended with the compressor unhooked.
Might not apply, but when i break my front struts they stay fully extended and will not move.