S211 Self Levelling Suspension

[SJHE]

Hi, I’m after a little bit of advice if possible regarding the self levelling suspension on my 211.

For some reason the car is down on the drivers side approx 10-15 mm. I actually hadn’t noticed until today when I had to take the rear wheel off for something else and spotted the rubber boot that covers the air bag on the drivers side is rubbing against the shock absorber whereas there is a fairly decent gap on the other side.

The previous owner had both air bags replaced about three years ago so I’m hoping this isn’t the issue. I popped the wheel arch lining out and located the compressor but I have no idea if it’s running over the noise of the engine. It didn’t seem to be vibrating to the touch but then again I’m not sure how often it should kick in. Where is the fuse located for this? And is there an easy way to test the pump or even reset the system? Or is it simply pull the air line off it and see if there is air flow?

As the one side seems to remain inflated, would it be a sensible assumption to think the pump is okay?

My understanding of the system is fairly rudimentary (probably already evident) so any insight or advice would be much appreciated. If I need a diagnostic, the nearest indie is 100 miles away so chances are I’d have to fork out for the main dealer as they're just down the road. With their prices in mind, I’d like to ty and cover the basics myself If possible.

Thanks in advance!

 

[ajlsl600]

Would have thought they go up down in pair front rear so valve that hold pressure in that side. Sensor that see level that side or leaking bag. Stand to be corrected. But how I wud see it

 

[M80]

On the 639 the compressor will run w/o the engine running. I hear it pumping up often.
I've never heard our 211 pumping up so maybe different. The 639 does have control buttons for raising / lowering so there is difference.
Maybe others might confirm.

 

[steveq]

Hi, I’m after a little bit of advice if possible regarding the self levelling suspension on my 211.

For some reason the car is down on the drivers side approx 10-15 mm. I actually hadn’t noticed until today when I had to take the rear wheel off for something else and spotted the rubber boot that covers the air bag on the drivers side is rubbing against the shock absorber whereas there is a fairly decent gap on the other side.

The previous owner had both air bags replaced about three years ago so I’m hoping this isn’t the issue. I popped the wheel arch lining out and located the compressor but I have no idea if it’s running over the noise of the engine. It didn’t seem to be vibrating to the touch but then again I’m not sure how often it should kick in. Where is the fuse located for this? And is there an easy way to test the pump or even reset the system? Or is it simply pull the air line off it and see if there is air flow?

As the one side seems to remain inflated, would it be a sensible assumption to think the pump is okay?

My understanding of the system is fairly rudimentary (probably already evident) so any insight or advice would be much appreciated. If I need a diagnostic, the nearest indie is 100 miles away so chances are I’d have to fork out for the main dealer as they're just down the road. With their prices in mind, I’d like to ty and cover the basics myself If possible.

Thanks in advance!

I would guess that one of air suspension units is leaking. Do you know if the replacements were MB or even a known brand? There are a number of spurious suppliers of questionable quality.
It could be a leak in the pipe work too. It is worth using soapy water to see if there are any leaks.
If you don't know the make of the new units, you might have to replace both so that they have the same characteristics.

 

[steveq]

The pump should only run to inflate the units which should be infrequent.
You should also check the level sensors as they can break

 

[WindyH]

Your airsprings should be the same make. I had this when a previously replaced Aerosus failed (they're crap) and I replaced it with an Arnott. Then car sat about an inch higher on one side. Only when I replaced the other with a matching Arnott did the car sit level again.. It's not just inflation height, it's pressure too. There will be slightly different pressures to get different makes of airspring to the same height...

 

[malcolm E53 AMG]

There is a pump repair kit if it’s not supplying enough pressure ie the piston ring is worn

Pardon our interruption...

If the pump is providing pressure I suspect you need a new airspring or an air line has chaffed through or split

 

[Snake Charmer]

My S211 had stood for long periods before my ownership and would sag slowly both sides if left a few days, regular use seems to have helped as it held for a week recently. I started looking at the system online to gain some familiarity to pre-empt any enevitable failure and found two schematics for the semi-active (rear only) air suspension. I need to get under mine and identify the components when I change the rear dampers this week.
From what I have seen of the system, each air spring has a one way valve on the air inlet and a solenoid controlled release to keep the ride height under differing load conditions. In theory, if they are connected together, a leak on one side should affect both sides as the pressure equals out.

 

[SJHE]

Thanks for all the replies. I tested the pump with a 12V battery today and it fired up just fine, as did the solenoid for the air release valve.

But when I connected it back to the car there was nothing. So I’ve ordered a relay and I’ll try this first an an optimistic easy fix. If it’s not this, it’ll be onto the level sensors as I guess there’s a chance these aren’t telling the car it needs to level itself up?

If that doesn’t work it’ll be time for a diagnostic to see if they can manually activate the pump as there’s no way of testing the system without getting the pump to run.

I will post an update in a few days after I’ve fitted the relay.

 

[SJHE]

Can anyone tell me definitively where the fuse is located for the pump as I’m struggling to find it. There are fuses in the end of the dashboard on the drivers side and there is a fuse in the “airmatic“ position even thought the car doesn’t have the “airmatic“ setup. Would this be it? The car is a facelift S211.

 

[Snake Charmer]

Have a look in the load space on the left hand side, mine is 2004 and has fuses with a whole load of gubbins in there. Do you have the handbook?

I measured mine tonight prior to changing the rear dampers and there was around 8-10mm difference per side.

 

[SJHE]

So I found a blown fuse this evening and thought I got lucky but it seems it’s for the cigarette lighter which was a disappointment to say the least.

I’ve also bought a relay from MB as swapping it out seems to be the next logical step but I can’t for the life of me find where it goes!! Can anyone please advise as MB were no help at. I’ve checked the fuse box under the bonnet, in the side of the dashboard and also in the boot but can’t find a relay with the same part number or diagram on it. That of course is assuming MB have given me the correct relay.

Part number is 4RA 007 791-52 A0009828523

All suggestions welcome!!

 

[Snake Charmer]

My iCarsoft CR Max cycles the pump then tells me the valve is faulty. I can feel the car rising and falling but no fault codes though.

 

[Snake Charmer]

I have had to delve deeper into the self levelling on my S211 as it started to drop on the r/h side then eventually the l/h when parked and has worsened to the point it dropped 2" sat on the Mot ramp last Saturday.

I found a few decent schematics of the pump and air spring cutaway etc but not much on the system operation. Two schematics showed different systems, both self levelling and not full Airmatic. My car has the simpler of the two systems; pump, 3 way tee behind the differential, two identical air springs and a height sensor on the rear anti-roll bar. At the moment, what controls the system I am unsure of, either the ECU or one of the myriad boxes of electrickery hidden everywhere. I was astounded to see what the tailgate contains when fitting a towbar!

The compressor is quite a bit more than just a simple pump, there is an air filter, desiccant air drier, non return valves, exhaust restrictor and solenoid air valves.
Each air spring has a solenoid valve that opens to let air in or out depending on the solenoid valves in the compressor and air exiting is passed through the desiccant drier and not simply vented to air.

Having a little more information, I removed the r/h air spring to see if the leak was repairable. With the outer gaitor removed, I refitted the air spring back on the car and the leak was louder, the bladder had gone. The corrosion on all the ferrous parts is horrendous so I suspect these are original at 178k miles.

I used my iCarsoft CR Max to open the air spring solenoids and dump the air, part of the test sequence is to hold them open for 20 seconds and works well with the air tube removed.
I am now waiting for a pair or Arnott A-2726 air springs, the piston ring repair kit from "Bagpipingandy" on Ebay has arrived so I will overhaul the compressor and fingers crossed all will be well for a week or two until the next bit breaks.

 

[malcolm E53 AMG]

The main issues with rear air suspension in order of failure are compressors, airbags and airline leaks not much else reported on here the valve block appears to be very reliable. Always worth trying the relay first if the compressor doesn’t operate I keep a spare in the car toolkit

 

[LostKiwi]

The main issues with rear air suspension in order of failure are compressors, airbags and airline leaks not much else reported on here the valve block appears to be very reliable. Always worth trying the relay first if the compressor doesn’t operate I keep a spare in the car toolkit

Also broken height sensors.

Lube the sensor links to prevent this.