E250 S212 Sagging at the back overnight

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DrNick

MB Enthusiast
Joined
Nov 25, 2003
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Location
UK
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SL500
My 2014 E class estate (with 30k on the clock) has started sagging at the back overnight, with the message on the dash "Wait - Car rising" or something similar.
It pumps itself up and off we go.
The first time I noticed this was a couple of days ago when I came back off holiday so the car had been standing for 2 weeks. I thought this might be normal and once it had pumped itself up that would be fine.
But no. It sags overnight now (on both sides - don't know if one side goes down first - I'm assuming both sides are linked and not independent)

I've looked at past posts and understand that somewhere there is a leak, but was wondering if it might have something to do with the hot weather and pressure increase in the system venting during the day, and it all cooling down overnight.
I suspect not though and the coming cooler weather will show me if this is true or not!

So does anyone have any insight into how I can identify the source of the leak (is it worth paying for a Star diagnostic) or is it most likely to be one of the airbags and I should replace them both as if ones gone, the other isn't going to be far behind.

Does anyone have any direct experience of the relatively low cost items available on Ebay sourced from China, or is there a better source that people have used.

The suspension is the standard estate suspension ie its self leveling, not full airmatic
 
I had a similar issue on my 2011 S212 E220. When I bought it over 18 months ago the rear would drop noticeably over a couple of days.
Each side dropped at different rates but if the car was left for 3-4 days both sides were right down with the wheels up under the arches.
I also got the message 'Wait - car rising' or similar.

I looked for leaks in the pipework and at the valve block behind the rear bumper by putting soapy water and looking for air bubbles.
I found none although I have heard of others where they found leaks in the airline.

Are both sides dropping at the exactly same rate --- I suggest that you measure the height of each side when you park, then again after a few hours, then overnight, etc. ?
If so I would be suspicious of the pipework.
If not then the airbags are probably leaking.
I am not sure if Star is of any use over and above manual observation.

It is a bit strange that it suddenly started happening

You will need to rectify it reasonably quickly as the pump will eventually fail from excessive use.

I replaced both air suspension units -- I wrote it up on 'the other side'.
I did the job on the driveway -- not easy (and certainly not advisable in the cold, short days of early January) but doable.
That solved the problem and I have not had an issue since doing it.
Search 'S212 Rear Suspension Dropping' if you want to read up about it.

I saw the ads on Ebay but ended up buying them from a different supplier at much the same price but gave a 2 year warranty and it was probably one that could be relied on -- I haven't had to test it (yet).
 
Makes sense. I'll measure the fall rate on each side. Thanks for your reply (I think I've read your write-up)
 
You're also correct on two items:

1/ If you can afford it - do both side to balance the car and for preventative maintenance..

2/ Stay away from Chinese if you can - cheap and nasty, only if you were selling the car or want to revisit in a few months time..
 
An update. The car sags more on the drivers side but it looks like the passenger side is also sagging at a slower rate. Are both sides linked?
 
I don't think they are directly linked to each other except through the valve block.
There is a level sensor which is located near the back axle which controls the height of both sides.
As I said above, I would say that if they are dropping at different rates it is most likely that the airbags are the problem.
I am only saying that because if the issue was elsewhere both sides would drop at the same rate.
I am also assuming that the car is on level ground.
The problem still could be the air lines to each airbag or the valve block at the rear bumper. Definitely worth trying the soapy water test on the lines from the valve block to the airbags and the valve block itself.

The one question that is puzzling is that your problem suddenly started happening. Were the 2 weeks' holidays the longest time it ever spent unused? With only 30K miles and 4 years old it must spend a good deal of time parked.
 
Mine occasionally drops or pumps up depends.

I went overnight fishing a couple of weeks ago, stopped the car switched off unloaded car the following day I got back to the car and started it up to get the air on working to cool the car and I could hear and see the car rising up.

I have also started car in garage and felt it rise up against my leg on an occasion.

I have always thought this to be normal behaviour.

I have had my car from new (2016) so will watch this thread with interest.

Robin
 
I thought that there was sensor either side?
Only reason is, mine was sagging slightly one side and Mercedes main dealer recalibrated passenger side height sensor
 
Well it is unlikely to be the height sensor because if that fails or is broken then both sides go down and stay down,because the sensor when it is broke tells the car that all is well and the car is at the right height,so when that happens it is a dead give away that the sensor has snapped or faulted in some way,you on the other hand are getting the back sag down over night but it pumps up in the morning,I would not get too involved with the back of the car at this time,your air pump is at the front passenger side it would seem to be working ok but it sends the air it makes to a small cylinder which is close by the pump from here the air is sent to in your case to the back air system,on most cars with this fitted you can see the small tank and pipework if you take the front left hand plastic wheel arch cover off or take the shroud off at the front underneath,I would check the pipe work here for a leak,because as I was told the small tank/sphere is what tops up the air suspension as it is needed as you drive along so the pump is not running all the time,maybe with the pump exposed and the car running you might be able to feel or hear if the pump is running all the time,this would point to a leak as well.
A star has the ability to check the pumps function in filling the sphere in a certain time a few seconds ,the star can empty the sphere and then start the pump,you might have to go this route if you cannot find a air leak,I would go that route before looking at the rear suspension.
 
As always, sensible advice on this forum. I'm pretty sure that its only the drivers side that is sagging. This means that there is a leak associated with the drivers side which could be anywhere from the valve block to the spring itself. I've had the car about 18 months and this is probably the longest its been left without use, so I wasn't too worried when I saw it was down. However, it now does it overnight so whatever happened appears to now be permanent and I guess is only going to get worse.
I'll talk to someone to see what can realistically be achieved with a computer. Soapy water on joints is an option if the joints are easily accessible, but I would guess that the issue is more to do with moving parts which does point to the spring or its connector.
 
I understand that the air lines can fray as they rub against the undertrays and other items.
With the quick onset of your issue and it being only one side, it might easily be a small leak in the pipe from the valve block to the suspension unit on that side.
I would remove all covers at the rear and thoroughly inspect and check for leaks. The valve block on the S212 is behind the rear bumper slightly on the passenger side.
 
Update: Its booked in to be looked at. However,since booking it, its decided to stop doing it. Whereas before it sagged completely overnight and probably 80% in the day whilst parked up at work, for the last 2 days its decided to not do it at all or very little. Oh well - a few more days for it to decide if its broken or not. Doesn't exactly correlate with the recent hot weather, but not far off. Maybe a valve was sticking, or a seal is starting to go. Nothing is ever straightforward with these cars!
 
Result !!
Keep muttering about a trip to the knackers yard every time you get in -- it might keep behaving !!
 
So hopefully the final update. No leak could be found the first time it went in, so we decided to leave it until it was more pronounced.
So it became more pronounced in the last couple of weeks and would sag completely afterr a few hours.
Local independent garage had another look and found a pipe with a small hole in it. Over time this had developed into a crack but it was in an awkward position and so wasn't easy to spot until it had developed.
The pipe has been spliced (apparently there is a special connector joint for this job). 2 days on without using the car and its still inflated!
Job done. Apparently MB can now supply refurbished airsprings if you want. We didn't need them so can't offer any more info on that.
 

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