Over the past few months, my 14 GL450 will sag all the way down in the rear within a few minutes of parking. It doesn't happen all of the time and I usually hear a hissing noise of air being released by the driver rear wheel when I park it (but not always).
It seems like this would be a valve getting stuck open or opening when it shouldn't since it isnt consistent, otherwise a leak would always cause it to do this.
Does that sound right? Is there a way to test this? I've tried getting underneath it when I hear the noise but I can't since it gets far too low pretty quickly to be able to diagnose it and it doesnt do the same thing when you put it on a lift.

 

There have been a few posts on this recently. I had a similar issue as you mentioned and the fix for me was the rear airbag replacements. Based on you hearing the hissing on the driver side rear, this would more than likely be due to a crack in the air bag. The way to test is to spray soapy water on the air bag while you hear the hissing and look for bubbling, sort of hard to have that handy and when to expect it to sag as it is not every time.

I went with the Arnott replacement. The job was easy and took about 30 mins per side. No longer sagging in the rear and it has been 2 weeks.

https://mbworld.org/forums/gl-class-...uspension.html

 

I replaced both of my rear airbags yesterday. It was a quick job that wasn't very tough. There are some good videos on Youtube on how to do it. I went with Bilstein air bags that I got for a little over $400 for the pair w/ tax and shipped from Rock Auto. It was nice to see the GL not sagged this morning and I will feel better towing with the rear at the right height and the compressor not working so hard.

 

Hi, I am having the same problem with mine and I took it in, they first replaced my valve block, said it was bad, did same thing, took back again and then they said it was the compressor so replacing that, another $ 1500 and now they just called and told me that both air bags have a leak and they need replaced. I was like WHAT?? So my question for you guys, is it possible the valve block and compressor is both bad along with both air bags leaking?? Please let me know, Thanks so much.

 

Hi, I am having the same problem with mine and I took it in, they first replaced my valve block, said it was bad, did same thing, took back again and then they said it was the compressor so replacing that, another $ 1500 and now they just called and told me that both air bags have a leak and they need replaced. I was like WHAT?? So my question for you guys, is it possible the valve block and compressor is both bad along with both air bags leaking?? Please let me know, Thanks so much.

 

Sounds suspiciously like guess and check on your dime...

For me, I didn't think I had a compressor issue because it would pump up the airbag when the car was on but the air would leak out over time when the car was off. The system knew when the corner was low and when it was pumped up so I didn't believe it was a level sensor. I figured my issue was either a leaky airbag or a bad valve/tubing. I tried to find an air leak using soapy water but didn't find anything. I read online that leaking airbags are the most common issue especially on older GLs and ones with >120,000 miles so I took a gamble and bought the air bags. Even if I was wrong in my diagnosis, it is still a ton cheaper than having a shop do it and the air bags would have probably been due to be replaced shortly anyways.

Hopefully the airbags do the trick for you.

 

Thanks for your reply. I also feel they are just trying to pull me as they try to figure out what was wrong, so hard to believe that the Valve Block was bad but when i took it home it was still sitting low after parked awhile. Ohhh now they charged me $ 1500 for the compressor and now they say both air bags have holes. I am not a mechanic but hard to believe all 3 things were bad.

 

From what I've read from many other people having airbag issues, once you have a leak in the system then the compressor starts working much harder than normal and can wear out too, as a secondary problem. So while it sounds like the mechanic's troubleshooting methods aren't good, I'm not surprised that they found a leak in the system AND a bad compressor. Also, what often happens with pressurized systems that have leaks (liquid or air), once you fix one leak, then the system pressure is higher than before and it can expose/create a new leak that wasn't apparent before while it was running at lower pressure. There's a chance they are screwing you by replacing parts that aren't bad, but there's a chance multiple parts really are bad. One thing you could do is to request that they give you the old parts, although bench testing them at home might be hard.

I was thinking that since tire shops find leaks by submerging a tire in a tub of water, it would be funny (and horribly dangerous and damaging) to troubleshoot the air suspension by driving the GL into a pool of water about three feet deep, then swimming around with a snorkel to find the leaks.

 

rear bags are under 100.00 dollars on amazon, throw a set in. It takes 20-30 minutes to do the pair of them. sometime you have to go in and reset ride height with scanner ( normally on a 550 with ads). if you have a scanner you can do a airmatic compressor test and see if it passes. normally we only have to replace the valveblock if the front end (one side or the other) does not pump up. I HAVE NOT yet replace a valve block for rear problems. And i have done a bunch of gl,r, s, gls with airmatics

 

Thanks all. I did spray soapy water and the rear driver airbag had a few leaks/holes. Bought a bilstein oem replacement and it was pretty easy to replace but the fitting from the tube into the airbag started leaking after a few days. Bought a new fitting and hope that fixes it otherwise will need to try and RMA the bag.

 

@BrendaMcCarson I am not sure if my experience will help you but let me try.

I recently changed my rear airbags as both sides in the rear were sagging just after turning the car off. The sagging was getting quicker and quicker, almost like whatever leak existed was getting bigger. Anyway, I did the RR first and then the LR. When I removed the airbag first in the RR, i was not able to get the airbag out. So I went to loosen the level sensor as someone else had done. I noticed that the bottom plate that holds the sensor is at an angle. I'm like, should there not be two screws holding this thing in place and the plate should be parallel to the body of the car? I did loosen the one screw, but tightened it up a bit, but left the plate the way I found it, at an angle to the body, not parallel. I was able to get the airbag out w/o removing the sensor.
Next moved onto the LR side. I was able to get the bag out, and this time I saw that the bottom plate of the sensor, also having only one screw, was parallel (correct position) to the body. However, there was only one screw holding the plate, when clearly, there is provision (a hole) for two screws.

After putting the fuse back, lifting the car by pressing the "up" button on the center console, all looked good. Went for a spin, things started out fine but not as smooth as before with the leaky bags. I parked the car in the garage, went to check the mail, and when I came back, the right side, RR side, was down. but the LR side was up like normal. I opened up the RR side, loosed the sensor plate, moved it to parallel to the body and the plate fell into a ditch to correctly sit into the lower control arm (I guess this is why there is no 2nd screw, but there should be one). Then I tightened the level sensor screw. Put the fuse back in, raised the car and brought it back down, and it has been normal since.

So my theory is, perhaps your airbags were bad as it is the common issue, but also your level sensor play may be loose or not in the correct position, parallel to the body.

hope this helps; or at least I got this theory off my chest. :-)

cheers.