Seems like there are a couple recent threads about the airmatic leaks/malfunctions, but those fact patterns differ a bit from what I'm experiencing.

My '19 GLS has relatively low miles (15k), and a few months ago it started to sporadically release all air out of the rear suspension when parked. The release is rapid (~15 seconds to completely deflate), and the first time it occurred was immediately after a rear passenger door was opened after the car had been parked overnight. Once the door was opened, the rear suspension completed deflated (accompanied by hissing sound). The car is daily driven, and I would say that 20% of the time that I walk up to the car after it has been sitting for any amount of time (whether it be 10 minutes or 12+ hours), the rear is completely deflated. Sometimes the car will be parked for a few days with no activity, and the rear suspension will maintain its correct/constant height. With these observations, it seems to me that there isn't a leak, but something else is triggering the rear to periodically, rapidly, release all air.

Could a low battery(ies) cause this? Perhaps a faulty ride height sensor? The latter seems somewhat unlikely to me, since the car does just fine when the engine is running.

As an aside, this car has had a couple bizarre one-off issues since I bought it (original owner). In one instance, a few years ago, the car wouldn't start with either the keyless start button or the key in the ignition. The car just wouldn't recognize the key. After 5 minutes it started and the problem never happened again. In another instance, the car wouldn't shift out of reverse. After shutting the car off I was able to get it in park, and everything was fine. Never happened again.

Thanks for your time.

 

The main 'distribution block' for the airmatic system occasionally does fail on these cars. It's under the car in the left rear corner. I'd have to bet that's what the issue is given it happens when you open the door which "wakes up" the system and wants to try and level the car.

 

Thank you for the reply. I've had a new observation since my original post. About two weeks ago I had all four tires replaced, which required the vehicle to be on a lift with all four wheels off the ground. For the next 10 or so days after the tire replacement, of which it was driven daily, the airmatic system kept a level ride height each time the car was parked. However, a few days ago I walked up to the car and the back end had dropped down, and it has returned to the intermittent/random dropping of the rear when parked... Could it be a ride height sensor, or do you still think it might be the distribution block?

Thanks again

 

That sounds more like the airbags are starting to leak. Mine started to and it ended up being basically like the rubber airbag started to rot and it developed tons of little pin hole leaks. If I sprayed soapy water on it, millions of little bubbles would start forming. New bags were $500 for the pair and I installed them myself in the driveway.

 

do you always drive in the same drive mode? I have been having the same rear sagging problem, with the air hissing etc, BUT it only happens when I drive in sport mode so the car starts off lower. No clue what the fix is.

 

I do, yes. But when the airbags raise and lower the car, the bag kind of rolls over itself, so when it's lower, you might be "exposing" a part of the bag that has more holes in it. All I can think of. If you can, get a spray bottle with some soapy water in it and spray the bag as much as you can, start the car and put it in sport mode and see if you can see bubbles. Should be on the bottom end of the bag.

 

What app or scanner did you use to fill the rear air springs?
I bought new springs for a 2018 GLS 550 and directions say 2011+ models need the springs filled by a diagnostic system.

 

No tool/system needed. To keep the airbag from constantly trying to inflate, just crack a door open which disables the whole system. When you start up the car next time, it'll inflate and get to the correct ride height automatically like normal.

 

Good news, at least for now. Replaced both rear bags and the system has been stable for the past 10 days. Bummer to have to do that at 15k miles, but I guess age and a dry climate too their toll on the vehicle.