E220 CDI S211 Rear Suspension issue

[atlantimd]

My S211 has an on going issue with rear self-levelling suspension. The car lowers during the night on one side only. There is a history with this car since 2021 left side lowers overnight

Both rear airbags were replaced and due to the left side still dropping after replacement I had both airbags replaced under warranty and I have the same issue with the new airbags. The replacement airbags are Aersus from Germany
Once the car starts in the morning the compressor lifts it by the 2” approx. I have noticed lately that the car is not level when parked with RH rear higher by about a half inch.
I carried out a lot of trouble shooting in 2021 and can confirm
I have checked airlines with soap water ok
Checked the one rear height sensor is intact not broken
Checked air compressor under left wheel arch ok
There are no extra air tanks on this model just the airbags on rear and coil spring on the front self levelling on the rear.

I have witnessed the car drop after being let down of a jack which is normal to level the car and you can hear the valve energise and de energise to release the air pressure
I believe that even if there were leaks in the airlines this would not be the problem, as the air should be held in the airbags overnight. For some reason the car is energising the air valve in the top of the airbag right side and releasing the pressure as there are no leaks.
I have icarsoft but not STAR can anyone confirm is there a menu in star where you can reset the rear heights although looking online the STAR menu looks like there is nothing to do this.
With the recent cold weather the car is lower in the morning I suppose that is to do with air density in cold nights
Any help would be great as I like the car but it will wreck the pump and does not look good in the morning sitting one side down with the wheel in the wheel arch.

 

[atlantimd]

I am not surprised I have no reply here. It seems to be a common issue with these cars and I don't think anyone has managed to get head around this.
I am thinking or intercepting the wiring to each bag so I can deactivate and power going to the airbag valve during the night. maybe put in a double pole switch on each.

 

[JeffHilton]

Sorry you've had no luck with this - it does seem to be a grey area. Mine can be fine parked for a week and then suddenly drop to the floor overnight, other times it'll drop every night. All very strange and I'm hanging on for as long as I dare before investigating. Seriously considering a coil spring conversion although it's not cheap.

Best of luck with yours.

 

[malcolm E53 AMG]

A lot of complaints regarding Aerosus airbags so I don’t think you can rule out a component issue with them. When the airbags deteriorate and start to loose air it’s generally when the car is stood depending on how it’s parked it may leak one night and not another. Arnott have a better reputation and MB offer exchange units which would be my preferred option

 

[atlantimd]

Thanks for the replies guys. I am not a fan of the Aerosus but in 2 sets it is alway the left rear. Both are the same part number so they could fit either side but my left side always drops.
I was thinking of the cold spring mod but I would be afraid of handling after fitting.
The fact my car is not level I was wondering is there sensors else where that is giving an input, I have seen 2 plastic sensor on front suspension but I have read that this is for headlight beam height.
Hoping to get it sorted as I have the bit between my teeth now.

 

[mioba]

Had an issue on my 251 a couple of years ago.
was advised by my indy to not consider aftermarket struts - cheap components wont hold the car up.
I went of course for gen MB and not an issue since.

MB do reman struts!

 

[MJJ]

I did a lot of diagnosis and reading when my 2008 S211 was doing similar. Despite having all of the Mercedes workshop manuals and parts fiches, I was never able to conclusively find out how the system is supposed to work. I am no expert, but this is the way I think the system works and perhaps some of the following may help you:

- Each airbag has a simple, mechanical one way valve (you can see it, just inside the inlet on the airbag) on the inlet, and an electrically actuated de-gas valve. Thus, if a correctly installed bag has ever inflated correctly, the only way for it to lose pressure is either a bag leak, or the electrical de-gas valve incorrectly opening. Leaks in the lines and the rest of the system should not cause it to drop overnight.
- The electrical de-gas valve on the airbag is a simple two wire socket that can easily be unplugged if you wanted to rule that out from your diagnosis. This is very unlikely to be the culprit in my opinion as it would leak quickly, not slowly.
- (Most likely in my opinion) If, when installing the airbag, you pushed the airline inlet in too far (8-10mm is the right distance if I recall correctly) - it will be always pushing open the one-way valve in the airbag and thus allowing pressure to leak out. I would be testing this by soaking the air inlet area in soapy water and watching for bubbles.
- When installing the bags, we are supposed to use Star to pressurise the system prior to dropping the car down off jacks/ramps onto empty airbags. Fully weighting empty bags is likely to damage them causing leaks. On mine, I did not have Star but very, very slowly dropped the rear until the compressor kicked in. With hindsight, next time I will remove the rear ride height sensor and manipulate it to fool the car into kicking the compressor in earlier.
- If a bag does have a leak, chances are it will be in a fold that will naturally be hidden at normal ride height - thus it is very hard to find the leak unless you spend time manually manipulating the folds and spraying soapy water in.
- In my experience, the car will not even attempt to raise the rear until it is hugely low, or *both* the ride height sensor reads 20-25mm too low *and* the car is moving. iCarsoft live data allows you to see the value of the ride height sensor.
- As you know, the car has just one ride height sensor on the rear measuring an average of the two sides. Thus, if the car is not level when parked, it is most likely a pressure difference in the two airbags - i.e. a leak.
- The compressor has a maximum operating time, presumably to stop it overheating. If it is not building pressure well enough, it simply won't raise the car up and it has to be almost at death's door before the car will display any errors on the dashboard. My car ran at c. 60mm too low at the rear bumper before any dash warnings triggered. A new compressor piston (£25 and 2 hours easy work) from bagpipingandy sorted it.
- Star diagnostics has a lot of great live data and test routines that DIY diagnostics does not - these, and a knowledgeable operator will get you to a root cause easily. Paying an indie with Star for an hour or two's diagnosis time here might be very wise.


From your symptoms, I am almost certain you still have a leak in the left side airbag - perhaps from the inlet pipe being pushed in too far. I think that your compressor is likely to be close to useless too as it has been working overtime since 2021. If it were me, I would be taking the left bag off the car and examining it very closely on a bench - after putting a little air in it (footpump, airline etc) to get some pressure and extension into it.

Replacing the piston ring is easy, and very worthwhile. Beware that if you *only* replace the compressor piston ring and not the leaky airbag, you may find that it now keeps up with the leak and fools you into thinking all is well - until the compressor fails again from working overtime.

These are hugely frustrating systems to work on, mainly because as soon as you jack up the car, it raises the ride height and de-pressurises the system - I found it best to have the car fully weighted on its wheels, but high up (lots of blocks of wood) so you can get under. It is an excellent system to cope with loads and towing when working though, so I would persevere with air personally.

Martin.

 

[malcolm E53 AMG]

I did a lot of diagnosis and reading when my 2008 S211 was doing similar. Despite having all of the Mercedes workshop manuals and parts fiches, I was never able to conclusively find out how the system is supposed to work. I am no expert, but this is the way I think the system works and perhaps some of the following may help you:

- Each airbag has a simple, mechanical one way valve (you can see it, just inside the inlet on the airbag) on the inlet, and an electrically actuated de-gas valve. Thus, if a correctly installed bag has ever inflated correctly, the only way for it to lose pressure is either a bag leak, or the electrical de-gas valve incorrectly opening. Leaks in the lines and the rest of the system should not cause it to drop overnight.
- The electrical de-gas valve on the airbag is a simple two wire socket that can easily be unplugged if you wanted to rule that out from your diagnosis. This is very unlikely to be the culprit in my opinion as it would leak quickly, not slowly.
- (Most likely in my opinion) If, when installing the airbag, you pushed the airline inlet in too far (8-10mm is the right distance if I recall correctly) - it will be always pushing open the one-way valve in the airbag and thus allowing pressure to leak out. I would be testing this by soaking the air inlet area in soapy water and watching for bubbles.
- When installing the bags, we are supposed to use Star to pressurise the system prior to dropping the car down off jacks/ramps onto empty airbags. Fully weighting empty bags is likely to damage them causing leaks. On mine, I did not have Star but very, very slowly dropped the rear until the compressor kicked in. With hindsight, next time I will remove the rear ride height sensor and manipulate it to fool the car into kicking the compressor in earlier.
- If a bag does have a leak, chances are it will be in a fold that will naturally be hidden at normal ride height - thus it is very hard to find the leak unless you spend time manually manipulating the folds and spraying soapy water in.
- In my experience, the car will not even attempt to raise the rear until it is hugely low, or *both* the ride height sensor reads 20-25mm too low *and* the car is moving. iCarsoft live data allows you to see the value of the ride height sensor.
- As you know, the car has just one ride height sensor on the rear measuring an average of the two sides. Thus, if the car is not level when parked, it is most likely a pressure difference in the two airbags - i.e. a leak.
- The compressor has a maximum operating time, presumably to stop it overheating. If it is not building pressure well enough, it simply won't raise the car up and it has to be almost at death's door before the car will display any errors on the dashboard. My car ran at c. 60mm too low at the rear bumper before any dash warnings triggered. A new compressor piston (£25 and 2 hours easy work) from bagpipingandy sorted it.
- Star diagnostics has a lot of great live data and test routines that DIY diagnostics does not - these, and a knowledgeable operator will get you to a root cause easily. Paying an indie with Star for an hour or two's diagnosis time here might be very wise.


From your symptoms, I am almost certain you still have a leak in the left side airbag - perhaps from the inlet pipe being pushed in too far. I think that your compressor is likely to be close to useless too as it has been working overtime since 2021. If it were me, I would be taking the left bag off the car and examining it very closely on a bench - after putting a little air in it (footpump, airline etc) to get some pressure and extension into it.

Replacing the piston ring is easy, and very worthwhile. Beware that if you *only* replace the compressor piston ring and not the leaky airbag, you may find that it now keeps up with the leak and fools you into thinking all is well - until the compressor fails again from working overtime.

These are hugely frustrating systems to work on, mainly because as soon as you jack up the car, it raises the ride height and de-pressurises the system - I found it best to have the car fully weighted on its wheels, but high up (lots of blocks of wood) so you can get under. It is an excellent system to cope with loads and towing when working though, so I would persevere with air personally.

Martin.

Which supplier did you use for airbags, MB, Arnott or Aerosus?

 

[MJJ]

Which supplier did you use for airbags, MB, Arnott or Aerosus?

I used Bilstein airbags, from a company called PFS Parts. They were £468 for the pair back in Feb 2021 when I purchased them. Very pleased with them.

Martin.

 

[malcolm E53 AMG]

Thanks Martin!

Just had a look on the PFS website and they’ve just added Bilstein airbags for the S212 for a reasonable £350 each so I know where to source them should I need any

 

[mioba]

Make sure your struts are ones with replacable bags. There was a crossover of struts around 2005 (atleast for the W220) which probably share the same PN. The later struts had the replacable bags otherwise its a new strut

 

[star]

There is only one level sensor and the system cannot be levelled side to side, a leak in the pipe work can be easily traced with soapy water spray. I would have thought it’s a faulty part, we started to use aersus replacement bags for the front struts on ml’s etc, only to find more often than not, they leaked. Oe from now on.

 

[atlantimd]

I did a lot of diagnosis and reading when my 2008 S211 was doing similar. Despite having all of the Mercedes workshop manuals and parts fiches, I was never able to conclusively find out how the system is supposed to work. I am no expert, but this is the way I think the system works and perhaps some of the following may help you:

- Each airbag has a simple, mechanical one way valve (you can see it, just inside the inlet on the airbag) on the inlet, and an electrically actuated de-gas valve. Thus, if a correctly installed bag has ever inflated correctly, the only way for it to lose pressure is either a bag leak, or the electrical de-gas valve incorrectly opening. Leaks in the lines and the rest of the system should not cause it to drop overnight.
- The electrical de-gas valve on the airbag is a simple two wire socket that can easily be unplugged if you wanted to rule that out from your diagnosis. This is very unlikely to be the culprit in my opinion as it would leak quickly, not slowly.
- (Most likely in my opinion) If, when installing the airbag, you pushed the airline inlet in too far (8-10mm is the right distance if I recall correctly) - it will be always pushing open the one-way valve in the airbag and thus allowing pressure to leak out. I would be testing this by soaking the air inlet area in soapy water and watching for bubbles.
- When installing the bags, we are supposed to use Star to pressurise the system prior to dropping the car down off jacks/ramps onto empty airbags. Fully weighting empty bags is likely to damage them causing leaks. On mine, I did not have Star but very, very slowly dropped the rear until the compressor kicked in. With hindsight, next time I will remove the rear ride height sensor and manipulate it to fool the car into kicking the compressor in earlier.
- If a bag does have a leak, chances are it will be in a fold that will naturally be hidden at normal ride height - thus it is very hard to find the leak unless you spend time manually manipulating the folds and spraying soapy water in.
- In my experience, the car will not even attempt to raise the rear until it is hugely low, or *both* the ride height sensor reads 20-25mm too low *and* the car is moving. iCarsoft live data allows you to see the value of the ride height sensor.
- As you know, the car has just one ride height sensor on the rear measuring an average of the two sides. Thus, if the car is not level when parked, it is most likely a pressure difference in the two airbags - i.e. a leak.
- The compressor has a maximum operating time, presumably to stop it overheating. If it is not building pressure well enough, it simply won't raise the car up and it has to be almost at death's door before the car will display any errors on the dashboard. My car ran at c. 60mm too low at the rear bumper before any dash warnings triggered. A new compressor piston (£25 and 2 hours easy work) from bagpipingandy sorted it.
- Star diagnostics has a lot of great live data and test routines that DIY diagnostics does not - these, and a knowledgeable operator will get you to a root cause easily. Paying an indie with Star for an hour or two's diagnosis time here might be very wise.


From your symptoms, I am almost certain you still have a leak in the left side airbag - perhaps from the inlet pipe being pushed in too far. I think that your compressor is likely to be close to useless too as it has been working overtime since 2021. If it were me, I would be taking the left bag off the car and examining it very closely on a bench - after putting a little air in it (footpump, airline etc) to get some pressure and extension into it.

Replacing the piston ring is easy, and very worthwhile. Beware that if you *only* replace the compressor piston ring and not the leaky airbag, you may find that it now keeps up with the leak and fools you into thinking all is well - until the compressor fails again from working overtime.

These are hugely frustrating systems to work on, mainly because as soon as you jack up the car, it raises the ride height and de-pressurises the system - I found it best to have the car fully weighted on its wheels, but high up (lots of blocks of wood) so you can get under. It is an excellent system to cope with loads and towing when working though, so I would persevere with air personally.

Martin.

Hi Martin thanks for your reply. You were helping with this same car in 2021 https://forums.mercedesclub.org.uk/index.php?threads/e220-estate-sls-the-drop.187831/
As mentioned before I inspected the Old air bags and the Aerosus units and there is no valve in them. These models have a electric operated Valve ( 12V for aerosol).
The Car has had 2 sets of Aerosus airbags fitted all drop on the left side. I don think there is any leak and the car ride height is higher on the right rear when car is running.

 

[atlantimd]

Is there an ECU controlling the rear airbags and does the height sensor have 2 sets of wires to control the air valves. I am thinking maybe change that rear height sensor just incase there is something giving wrong signals to release air pressure from the left airbag.
It is just strange that its alway the left side effected.

 

[alexanderfoti]

I am not surprised I have no reply here. It seems to be a common issue with these cars and I don't think anyone has managed to get head around this.
I am thinking or intercepting the wiring to each bag so I can deactivate and power going to the airbag valve during the night. maybe put in a double pole switch on each.

We have diagnosed a car recently with the same symptoms, no external leakage.

Fault was in the valve block, replacement cured it!

 

[atlantimd]

We have diagnosed a car recently with the same symptoms, no external leakage.

Fault was in the valve block, replacement cured it!

Thanks for your reply. My S211 estate model is the self levelling suspension which has no valve block. I think valve block was Airmatic models.

 

[alexanderfoti]

Sorry, wasn't paying attention! so it is.