S211 self leveling suspension issues

[sverker]

I have a S211 with self leveling suspension, i.e. air springs in the rear. Over the past years I've been having reoccuring issues, it started fall 2021 with the right spring blowing with a loud bang. I was able to make it to my parents house but it was a bumpy ride. I got a pair of replacement springs and a local workshop (my cousin's) were going to replace them. Due to time constraint he could only change the right one so I was going to come back another day so they could change the left but since that's 200 km from where I live and the system was working as it should I never got time for it. However since that episode I got a warning message of a disturbance on the air suspension and a fault code on the left spring.

Fast forward to late summer 2022, then again when on my way to my parents place the right spring lost air just a few km before arriving. This time I took it to a workshop specialized on MB with a good reputation, they made a thorough effort on troubleshooting but could not find the root cause on why it displayed the warning message and set a fault code. They changed both air spring (the right was broken which was the reason why it lost air), the control module and measured the wiring between the module and the springs. Still the warning message and fault code was there. Since the suspension worked anyway I didn't want to spend more money on troubleshooting then, and I needed the car.

Fast forward again to last week when it lost air on both sides, forturnatly just a few km from my home but it was a bumpy ride to get back. This time I spent some time on troubleshooting myself and concluded that the compressor while running didn't pump any air. There are rebuild kit for it, but that would have to be ordered from UK and I found a local company 20 min away that had a new compressor in stock which I could pick up today. Replaced the compressor and wanted to test it before I put back the wheel well and wheel so the car was still jacked up on left front.

Started the car, the new compressor pumped up left rear but right rear was low although with left front jacked up it would press down the rear right. Since the compressor obviously was working fine I put back the well and the weel. The right rear was still low, it raised and lowered like it was trying to adjust. Took it for a test drive and it behaved normal, ie. no bumpy ride at all. However, right rear is still lower than left rear.

My question is, since there to my understanding is only one height sensor how does the control unit know that the car is level? If it's high on left and low on right the sensor would still report the correct average height. As I understand the procedure with Star is to command both air springs to bleed and then pump them up on a level surface so that they'll be even. I tried to jack it up on right rear but that didn't fool the system, it still lowered the right side. Of course it's possible that it was the right spring that broke again and with the extra strain the compressor died. After all, this car has 470 000 km (close to 300 000 miles) and I think it was the original compressor so it is understandable.

The warning message I've had on suspension went away when compressor was replaced, so it seems the control unit is satisfied even though the car is not level. Is it necessary to connect Star to align it or will it self align? Unforturnatly I just have an iCarSoft unit which doesn't have the function to bleed the air springs.

 

[Nod]

I have just had fun and games replacing numerous rear air struts on both my x2 s211's. They had various issues, from leaking valves to small punctures and slight perishing. I experimented fixing them and also fitted some new ones along with a combination of old solenoid valves and new air struts. Some of my repairs failed after a period of time so I had to have the air struts on and off about x5 times, which wasn't a great experience but it did get me quite good at changing them, repairing them and working out certain issues.
As for self aligning, I believe it will automatically self align and is no need for Star. I also have Icarsoft MB2 and as you say no option on there to bleed etc, although the live data is useful on the 'Suspension' module and also the live data 'Front Headlight Aligning' tells you of ride heights which is useful to work out if the bags are up nice and high. Mine seemed to always just align itself each time I put a new airbag on one side, when they were totally uneven with one bag being inflated and the other(new one) empty. I think the car has to be started to set the compressor off, some people think opening the doors sets it off but in my experience it does not, on mine I think the engine had to be started. Also the compressor will not come on if you have it hooked upto the Icarsoft and are interrogating the suspension module at the sametime. So start the car, let it inflate for a few minutes, then plug the Icarsoft in to check the levels etc. Cannot remember if it does left and right ride heights, it maybe an average as you said between the two sides, still useful though for seeing what ride height you are getting, the lower the number, the higher the ride height. Think anything under 10mm is a nice height, mine is now as high as 6-8mm which I am pretty pleased with, when it was leaking it was showing about 14mm and sitting low.

I still have a small leak in oneside but the repair on the otherside is really good and the car rides lovely and high now, albeit with the other side slightly dropping over night. Its not that bad to warrant changing it yet and can live with it.
As you say you have to be abit careful as if the air strut leak is bad then the compressor can work overtime and get burnt out. Worth addressing as you really do not want to be buying and having to fit another compressor. I bought a spare on the other month, just in case mine have got overworked, as my leak was left for quite a while without addressing and think the compressor probably did work abit overtime... fingers crossed it did survive it.
Quite pricey to buy a pair of decent bags, I used the Aerosus replacements on mine, really do not like the threaded plastic valves though, so easy to strip. The new Aerosus bags have a metal insert on the valve thread, which is a vast improvement over the plastic type threads.