I'll preface this with: I have not pulled the codes yet, as my 12 yr old OBD2 reader isn't up to the task. A proper scanner is enroute, but I do not have it yet.

2014 GL450, 101k miles. I'm quite frankly not sure if what I'm seeing is normal operation, or will help with my troubleshooting, so I'll ask those who know better than me. I'm a car guy, work on and fix my own stuff, but this is my first Mercedes, so some things are new, namely, Airmatic.

I've had it for about 2 months. I've noticed 3-4 times in that timeframe, the Airmatic "Malfunction" error will pop up on the display. It's while I'm sitting still typically, no additional load, etc. This weekend, I picked up about 1,000 pounds of topsoil bags for a backyard project, and as I was driving home, the error message popped up again, and I realized that the back end of the vehicle was bouncier than usual. When I got home, I got out to check, and sure enough, it was sagging under the weight.

My questions and observations so far:

1) Is it a correct assumption that the suspension air compressor should have aired up the rear to compensate for the additional weight without any input from me? That's my understanding of how it is supposed to work.
2) I checked the system this morning, using the manual raise/lower button on the console. It appears to be going up and down fine, albeit very slow (several minutes just to go 1" in height), and it paused several times with the message "Compressor is cooling", again, on the way up.
3) How long should it take on average for the Airmatic to raise or lower? Also, does the compressor typically have to stop to cool?
4) In my 2 months of ownership, none of the shocks have sagged or are sagging, and have never displayed this behavior. The only real issue I can discern is that the back isn't self-leveling with additional load. I did search but didn't find anything that addressed this specific issue.

Based on my initial observations, I'm almost of the opinion that the air compressor is on its way out. I intend to wait until I get the proper scanner in order to do additional and detailed troubleshooting before tearing anything apart, but it would be helpful to understand a few of the system basics as I've noted above.

Thanks

 

Some of your airbags are leaking, that causes compressor to get hot. Rear bags are cheap to buy and easy diy to deal with. If you will keep driving as is it will kill your compressor.

 

Thanks for the feedback. So if the front are leaking, then that's not nearly as simple a replacement. Are just the bags easy to find front and rear? *off to Google*.

Thanks,

 

Ok I finally pulled the codes and unfortunately they are generic codes, so do little to help with troubleshooting. I'll be digging deeper into the disagnostic tools on the scanner I got to narrow this down. I prefer to troubleshoot the problem than just throw parts at it.

C156C00: The compressor distribution system is leaking.

C157200: The correction time when filling is too long.

 

Raising or lowering the suspension shouldn't take more than a minute. There aren't sensors on the bags themselves, so the system won't give a "rear left airbag leak" error message. I know you said you hadn't seen the rear end sagging, but if you're driving it daily it might just be pumping itself up all the time. Can you hear the compressor running often? It shouldn't be, if the system is leak-free. Have you ever left it for a few days, and measured the sag? If you've only had it a couple months, maybe it was ALWAYS sagged down a little, and you just didn't realize it wasn't supposed to be that low? Put it in the raised position when you park it, and measure the gap between the tire and fender on all four corners and see if it holds overnight. Have you checked for leaks at the air line fittings with soapy water or some leak-detection stuff? That should show any leaks.
I'm curious to hear what ends up being your problem, my 2013 GL450 has 108k miles and I'm planning on replacing my original airbags this year as a preventative measure.

 

Thanks for the suggestions. I've been outside with the Autel plugged in doing some testing. I haven't aired it up and let it sit overnight in high position. That's a good idea. I'll do that tonight. It has sat for approx two weeks one time since I got it, and there was no sagging.

A couple of things I noticed while messing with it outside just now.

1) When I turn on the compressor, it is pretty loud. Not so loud that I can hear it when the car is running, but with the car off and actuating it from the scanner, it's pretty loud. Is it supposed to be loud, or more of a whisper quiet?

2) I aired down the left and right rear, no problem. When I got to the front, it started to air up, and the compressor started cutting out. I then got an overheat error on the compressor. I'm not sure what the threshold there is, but surely it should be able to air up three bags in short succession without overheating. Maybe not.

I'm beginning to lean towards a weak air compressor, but I'm not sold on that yet, since I do have an error for a leak in the system, but at the same time, it hasn't aired down a noticeable amount ever, since I've had it.

More to come.

More to come.

 

Air bags are wrapped around air rubber sleeves. Sagging over time is 100 percent end of it time. Could be small leak under wrapped part of it, which only happens then you drive.
If the compressor overheats - it has to be rebuild or replaced either way - because it been handling your leak for a long and almost dead since it is not designed for long pumping.
If buying original compressor part out of your pocket - buy Chinese knockoff on Amazon, will work just fine.

 

This might be a stupid question but what do you mean by "using the manual raise/lower button on the console"? I have a '15 GL350 and I don't think my car has this button.

 

Further testing and I've found the following:

I'm not convinced I have a leak. I let it sit all weekend, and it has sat for as long as 7 days recently, and there is no drop in level, at least enough to notice. Even if it were a small leak, over that period of time, it would drop level I would think.

Using the Autel, I checked the pressures at all four struts. It varies from 6.73 bar to 7.00 bar, which is within spec.

The pressure in the central reservoir is another story. In researching, it looks like that should be 13-16 bar. Current reading is 3.16 bar.

While I acknowledge that a leak would cause the compressor to overwork, if there were a leak, at some point the suspension would sag, especially given the length of time I have let it sit a few times. It has never sagged in my two months of ownership so far. It would seem the compressor is wore out given the bar pressure reading, the compressor overheat reading, and the fact that since I cleared all stored codes, the only code to return is the overheat code.

 

I had similar issues before my left rear air bag went south causing the rear to slowly sit on its back end like an elephant. I replaced both airbags and the compressor (I figured since I was down there, I may as well do it and it wasn’t overly expensive or complicated) @ around 110K miles. All were relatively inexpensive Arnott products and almost too easy to remove and replace (R2).

I performed the R2 at home in my garage in 2018 and have put another 50K on it and it floated at speed like it was new until earlier this year my front suspension started to creak on the drivers side.

In late April of this, I started seeing the compressor malfunction indicator again and now my front end is sagging and sits on the stops. I’m prepared to do the R2 of the front air struts except I haven’t been able to get the driver side strut for going on 2 months now neither the OEM or the self-adjusting Arnott struts. According to my local dealership there are 125+ drivers side struts on back order at MB parts so my GL sits and waits.

 

I did a quick search on fcp euro and they had many front air strut assemblies marked “available”. Not sure if that’s accurate but worth checking out.

 

Wondering if you had any success? I am having similar issues and am interested in what you found.

 

I replaced the air suspension compressor two weeks ago and that fixed it. I have had no error messages since, and it is leveling correctly as it should now.

 

Hey GL driver it sounds like you have a short to ground I would have to see it in person to know more