Check for leaks @ strut, compressor valve, rear distributor pressure lines, and strut condition. All fine, could be internal fault.

 

I replaced both rear air bags, lines and fittings and leak checked all connections (bubble tight). The car held level for two days and when I looked at it this morning it's lower by one inch (25mm) on the left side again. The drop is significantly less than before, but still there. All connections at the compressor were checked too. What is the scheme for leveling the car out? Is there an internal valve for each air bag that levels the car out? It's not the hose or the buffer tank attached to the air bag as those were both leak checked when I replaced the air bag.

 

You can have an independent using MB Xentry (diagnostics) run system through leveling process but a certain amount of suspension drop due to thermal contraction is normal and should not be regarded as a malfunction. Approximately .75 to 1 inch of suspension drop in cold temperatures is within design parameters.

 

Thanks for the help....much appreciated. My concern is that it ONLY DROPS ON THE LEFT SIDE REAR!!! The car sits in a garage and when it drops, I'll start it up to level it out and leave it in the garage (Same temperature day and night as it's a heated garage). I haven't driven the car on the road since I replaced the bags as confidence is not high that it'll stay up on BOTH rear air shocks. And when it does ride low on one side there's a significant pull on the steering wheel as weight distribution on the four corners of the car is disturbed. In fact my tire pressure indicator says that I have a low tire pressure indicating that a tire is carrying more load and , in theory, is a smaller diameter and triggers the tire pressure monitoring system error due to a smaller tire spinning faster. Since the supply for the rear air bags from the air compressor tees off at the rear differential, then pressure should be equalized for each air bag and the car should stay level. No??? What controls the release of air in the shocks if the car ride height is changed? I'm ready to throw in the towel on this car!!

 

Internal solenoid, see rear air spring image in post 2:

 

Let me start by correcting myself....the rear right side drops and the rear left side stays up...sorry for the confusion. I'm assuming your answer of "Internal Solenoid" references my question "What controls the release of air in the shocks if the car ride height is changed?" They're brand new air bags on both sides. If the solenoid is energized and it releases air on the right side (sagging side) does this mean that the solenoid is not working on the left side because it stays up? Why would the car take such a significant drop 1-1/2" (38mm) on the right side over just a few hours?

 

OEM replacements are only available as remanufactured and not new hence chance of internal valve malfunction/leak. No apparent external leaks, have someone pull fault codes using Xentry (MB diagnostics) this should identify faulty strut, level sensor, etc. otherwise you will be chasing parts. Review attachments for a full understanding of system rather than me explaining piecemeal.

 

Thanks so much for the diagnostics diagram and parts list....this should be enough to get me in the ball park!!!!

 

I've been having a similar situation--my car has been 3/4 in higher on the left side, both front and rear, for at least three years. The car settles down over night, still one side higher, but lower with the same proportion. I've had both front struts replaced in the last two years, so it's an independent issue. The dealer and an independent shop have run the diagnostics three times on the computer, each time coming back "in spec" when it's visually not, and no leaks either. My indy finally figured it out--he said the level sensors are working but the airmatic control unit needs to be reset with a Rommus gauge, which the dealer has. For some reason, it thinks the car is 6mm too high on the low side, and 1mm too low on the high side!

 

You can view attachments in post 8 above and I added additional here to check for leaks @ rear, valve, etc. If you cannot view PDFs download free reader here: Adobe Acrobat Reader DC Install for all versions

 

AİRMATİC BEYNİNİN CONTALARINI YENİLEYİN SORUN KALMAZ GÖVDEYE GİREN BEYİNLER
LEAK CAUSES IF YOU DON'T RENEW THE GASKETS OF THE AIRMATIC BRAIN

 

AİRMATİC TAMİRİ BENİM KANALIMDA VARTHERE IS AN AIRMATIC REPAIR ON MY YOUTUB CHANNEL, YOU DON'T NEED TO HAVE A COMPLETE CHANGE BUY THE OUTER BODY AND TRANSFER YOUR OWN BRAINS BUT YOU NEED TO FIT NEW GASKETS.