S211 estate self levelling air suspension

[WindyH]

I've a 2008 model with self levelling system at rear only. For the past few months, it would drop at the rear n/s only repeatedly for a few days, then behave for a few weeks, then play up again, then behave again, etc. Only rear nearside would drop and never were any warnings displayed on the dash. I suspected a faulty release valve within the n/s spring. Having read the many posts on here, I decided to have a go myself and replace both rear air springs before the compressor expired too.

So I obtained two from Aerosus. Fitted them both today using a trolley jack and axle stands on the drive and after a bit of cursing and swearing when everything was back together, fitted wheels and lowered car on trolley jack to what I would consider to be 'normal height'. Started the engine and 'malfunction' for the air levelling system lights up. Ran the car for about 10 minutes but would go right down to bump stops on both sides if I lowered jack. Can't hear compressor running or any air escaping, I'm assuming that the system has detected a fault and shut down.

So I need some advice please - can I bypass the control system to put 12 volts to the compressor to see if it pumps up and holds pressure? If so then at least I can use the car for work on Monday..
I daren't remove the trolley jack and move the car as I don't want to pinch the deflated bags as other have said about. And which code reader should I invest in to reset the system? Other things to tell you: I didn't disconnect the battery while doing this but did it without the keys in the ignition. And I had to drill into the old air springs to release the pressure so that I could ease them out. Thanks in anticipation... Greg

 

[Borris1954]

I used SDS when I changed mine to run the compressor and inflate new springs one at a time but others on here have done it by bridging the compressor relay. If you do this I would suggest a fused link is used ideally with a push button switch. This allows you to run the compressor without the engine running so that you can clearly hear it running and also any air escaping.

Good luck sorting this.

PS silly question but you did remeber to plug the connections back into the solenoid valves on tge new springs.

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[WindyH]

Yes, connections plugged in, everything checked and double checked! In all the air spring posts no else seems to have instigated a "malfunction' message.

 

[WindyH]

So an update, it might be help to someone else at some time:

The levelling control system had shut down with the malfunction message showing on the dash. So my intention was to get enough air in to the new springs so that (a) I could at least use the car meanwhile and (b) so that the weight of the rear of the car wasn't sitting on deflated bags, as this can damage them. I disconnected the main power feed to the compressor and using a spare 12 volt battery, leads and croc clips got the compressor to run on its own. However, the airsprings need the internal valve to be open, this only happens when a voltage is applied via the 2 pin connector, you can't pump them up when disconnected. But the control system had shut down and wasn't giving any volts.... So I first dismantled one of the old springs and using a bench PSU could hear the valve click open at about 3 volts, polarity seemed not to matter. So extension lead and said PSU out on to the drive, disconnect the 2 pin plug and apply 3 volts to the connector pins on the spring (I found an unused 2 pin plug of the same type on the wiring harness under the bonnet so nipped it off to use) and at the same time as applying 12 volts to the compressor, I was able to inflate the springs, slowly, one side at a time.
It was a bit trial and error as I didn't want to over inflate them but I was soon able to remove the trolley jack and the car now sat on air, although a little lower than normal but I could bounce the back of the car up and down.
I re connected all the connectors and put everything back together, intending to visit my local garage asap to get the fault codes cleared and this hopefully kicking the control system back in to working again. However, on starting the car up again the malfunction message had gone and all is now working fine. Took the car for a good run and it is now sitting nicely, same hub to arch measurements on each side and correct looking ride height. If I opened the tailgate and sat my 16+ stone on the boot floor, I could feel the car rise.

All the 2 pin connector on the spring does is operate the internal air valve, that's it, no sensors.. This is why the airspring when venting does so back down the pipe through the compressor, it's down to simplicity and no doubt cost. When the valve opens, if the compressor is running the spring inflates. If the valve opens and the compressor isn't running, pressure will release and the spring deflates.

I've learnt a lot about this self levelling system from those who have posted before and from my own experience. Its not smoke and mirrors but quite straight forward.
The springs from Aerosus with optional next day delivery cost £505, I spent £40 on tools/kit needed and it's cost me the best part of a weekend, some knuckle skin but I'm pleased with the outcome. The Aerosus springs look 100% identical to the Merc ones and have a 2yr warranty, fingers crossed!

 

[Borris1954]

Well done on some good empirical work from first principles. I think what you have done using your workarounds is not a million miles away from what SDS/Star does i.e. opens the solenoid valve one side at a time and runs the compressor to inflate the spring. It also does it in stages.

Result!

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