I am sure this question has been asked in the past , however I can not find any real answers. So here it is. I bought my E about a year ago with 72K miles on it.
Since day one it has had a little hiss when I turn it off, but nothing else.

Fast forward to June 2017.
While on vacation in California ( I am an AZ resident) I came out from breakfast to find the rear on the ground. I started the car and it raised (lucky me)

No problems afterwords until about a week ago when the car lowers it rear only when it is shut off. I have the rear seats down and do not hear the compressor while driving.

Could this be a sensor, and if so where are they located? Again everything I have read only mentions the bladder and nothing else.

Thanks all in advance for any helpful thoughts or information.
J

 

Micro cracks in rubber could cause that , its a known issue.. especially if its cold outside it leaks faster...when it gets a bit Warner you cant even notice. That be my guess , from my past experience.

 

Both bags failing at the same time is low probability.
Bad news is you need good scanner to read anything on the system. Checking the line pressure holding would be the first point.

 

It can be very hard to pinpoint the problem with an airmatic suspension. I would recommend you to take your car to a Mercedes dealer for diagnostic. You will pay for one hour ( $175 or so ) but you will get a loaner vehicle, and they will be looking for the failing component as long as it takes. In my case, it took the dealer more then a week to find the problem.