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Problem with 2016 C350e Airmatic Suspension

Discussion in 'Suspension, Steering & Brakes' started by Martin Hedges, Oct 15, 2020 at 6:25 PM.

  1. Martin Hedges

    Martin Hedges New Member

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    Your Mercedes:
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    Wonder if anyone can provide some suggestions for the cause of my suspension problem

    I have a C350e which is 4 1/2 years old. DOne just over 60K miles

    Last week when drive the children home from school the back end suddenly became very bouncy. No warning message on the dash board. I pulled over and checked and the suspension was right down on both back wheels. Looks fine on the front. I got back in the car and switch the ignition back on and it came up vehicle rising on dash display. Suspension came back up to normal level and drove home fine. I went out it in later in the evening and was all fine.

    Next morning, on the way to school, got a dash message stayin STOP - SUSPENSION LOW. Before I had a chance to pull over that disappeared and when I did pull over (maybe a minute later) The rear and front suspension looks fine. Even when the message was on the car drove fine leading me to think that it was a false warning but I dont know for sure.

    On the way home from school that evening, it did the same thing it did the evening before - back became very bouncy, no warning message but rear suspension low (wheel arch over the tyres). Again came back up when I stopped and started and pressed the suspension up button. I could hear the compressor kick in so that seems to be working.

    The car was not used from Thursday to Tuesday due to the issue, during which time the suspension stayed up where it should, so it seems the issue isnt a leak on any of the air springs. Similarly, when I switch the car on on Tuesday to take to get fault codes read, I didnt hear the compressor kick in, suggesting, as far as I thing, that the air reservoirs not leaking, because if they were surely the compressor would kick in to refill them.

    On the way to the garage (less than 5 mins from home) the dash warning message to stop again came on and this time the rear suspension definitely dropped right down. Again, though, when I pulled in and pressed the raise suspension button, it came back up and was fine for the remainder of the 8 mile drive to the garage.

    The code reading didnt give any errors for the rear which is what has been dropping. Apparentlly there were codes for out of range for the front suspension and also an error for the compressor taking too long to raise the height.

    Based on the symptoms, and that the compressor seems to be working and raising the car, and that it is an intermittent issue, my conclusion (before error codes read) was that it was either a sensor issue - system thinking rear is too high and dropping the rear, but doesnt pick up the change and therefore keeps trying to drop it. However, the fact that the error codes dont indicate a problem with the rear suggests that is not right. The other possibility was that it was a blead valve sticking open - the system was opening a valve to lower the suspension and that was sticking, leading to the read dropping completely. That would then lead to the compressor taking to long fault as it would be trying to bring up but the air put in goes straight out. However, the fact that the car was not warning when the system was too low the first 2 times it happened would suggest otherwise, unless, of course, it is both.

    The technical info which the guy at the garage has managed to get apparently points to the compressor leaking somewhere but I cant quite get that unless, I guess, there is a valve sticking open which is allowing air to feed back from the rear springs and causing them to drop, but that would be an issue at the valve manifold rather than the compressor surely.

    I am thinking this is one of those issues that if someone has seen the combination of symptoms before they might be able to help.

    If anyone has any thoughts with logic to link it with the symptoms I would be very greatful
     
  2. V6Matty

    V6Matty Senior Member

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    I would have to guess at a level sensor coming adrift, sticking or feeding duff information. Get it on a ramp and check all the links and liberal spay of ptfe or similar. If it happens again then I would go the route of an Indy and live data while driving to see what’s happening.
     
  3. John Laidlaw

    John Laidlaw Senior Member

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    Welcome- can't add much to the above really, doesn't seem hardware related by your description of events
     
  4. OP
    Martin Hedges

    Martin Hedges New Member

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    Thanks for the replies.

    I have taken it a local garage (not a dealership) and they have plugged it in and there are 3 fault codes:

    C157200 (The correction time when filling is too long)
    C156782 (The Left front vehicle level is out of the permissible range. A Signal is below the permissible limit value)
    C156984 (The right front vehicle level is out of the permissible range. A Signal is below the permissible limit value)

    They took it out for a test drive and couldnt get the problem to repeat.

    The confusing thing with these codes is that it is the rear and not the front which is dropping. The front seems fine. Also, the compressor kicks in and the level comes up when the raise button is pressed.

    I am thinking maybe there is a valve which is sticking open which is dropping the suspension and the correction time is too long is the compressor trying to raise the rear after it drops but failing because a valve is stuck open and hence the air put in is being lost. The fact it is intermittent to be points away from the compressor as if that wasnt applying enough pressure it would do it all the time and the issue would be occuring constantly.

    Also, if it is a sticking valve, why is there no too low warning when the rear dropped the first two times. surely the system should detect that and warn?

    The place I took it to (and who have the car at the moment) which was recommended to me by a friend and who are, I believe, competent and honest, are scratching their head at the moment. When I contacted then I said what the system is as I was wanting somewhere who would be famiiar with the Merc system and hence more likely be able to tie the symptoms to the fault, but I am wondering whether they dont have that experience.

    Anyone know the system who can make any suggestions based on the above?

    Thanks again
     
  5. malcolm210

    malcolm210 Senior Member

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    Most probably the rear airbags leaking, they tend to leak intermittently depending on usage and of course stay up sometimes when the car is stood - plenty of threads on this if you do a search but usually on E class. Mercedes had a bad batch problem with the early 212 estates 2010-11
     
  6. OP
    Martin Hedges

    Martin Hedges New Member

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    Thanks. This a 2016 car so if the bad batch was 2010-11 then unlikely to be on mine??

    Also, it seems unlikely that airbags on both rears would go at the same time, that if the leak was so bad that it drops as quick as it does but then both dont leak when stood stationary before both leaking again at the same time?? Correct me if you think my logic is wrong but if a leak was enough to drop it like it does then it is unlikely it would not leak at least a but over time when stood stationary??
     
  7. Srdl

    Srdl Senior Member

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    Welcome Martin. Where are you based? We may know a reliable Indie you could try.
     
  8. OP
    Martin Hedges

    Martin Hedges New Member

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    North Northampton near Market Harborough and Kettering (very close to J 2 of A14). Northampton is also ok to get to but not quite as close.

    I have an engineering background but I think it is my ignorance of how the system works and is connected that means I am struggling to understand there the problem could be. As I said in my first post, in my mind the symptoms point to a sensor issue but as there are separate sensors on each wheel it would seem that both rear sensors must be playing up which seems unlikely unless there is common wiring or common routing which might be damaged. Also the fact that it is the rear which is dropping but the fronts which have the out of range error codes (If the rear sensors were not working at all surely there would be an error code saying that).
     
  9. malcolm210

    malcolm210 Senior Member

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    It’s fair to say you have a serious leak either from the plastic piping to the rear airbags (they can split) or more likely an airbag(s). The point I was making earlier is that MB do have a history with bad batches of rear airbags so don’t rule it out even on a 16 plate car.

    You really need the car in the air to check the rear axle level sensor and pipe work, I would imagine the front sensors are recording the symptoms and not the cause
     
  10. OP
    Martin Hedges

    Martin Hedges New Member

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    OK. Understood. Thanks.

    Is it really possible that there could be a serious leak which from an airbag or pipework (other than a sticking valve) which only leaks intermittently?
     
  11. malcolm210

    malcolm210 Senior Member

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    Airbag leaks leave a lot of people scratching their heads they tend to be intermittent some leak while the car is in use and some when the car is parked up.
     
  12. EmilysDad

    EmilysDad Senior Member

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    Though only one front corner of my R Class used go down, the rate of fall used to vary. Sometimes it'd stay up when left for a day or two & other times it'd go down within a few hours. And of course, according to MB they could never find fault when I returned the car to them but obviously it'd go down within a matter hours on my drive!
     
  13. Blobcat

    Blobcat Moderator

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    Agreed, the smallest cut can leak with movement but close back up again when parked.
     
  14. OP
    Martin Hedges

    Martin Hedges New Member

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    OK. But if there was a leak then the car would surely warn that the suspension was too low, whereas the first two times it happened the suspension on the back was bottomed out but there was no warning message from the car, which to me points to sensors
     
  15. malcolm210

    malcolm210 Senior Member

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  16. OP
    Martin Hedges

    Martin Hedges New Member

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    Thanks Malcolm210. That is very interesting. The fact that there is possibly a single level sensor for the back makes this consistent with the fact that the suspension is dropping on both rear wheels and if the sensor is playing up rather than completed U/S then that would be consistent with being intermittent.

    One things that has occured to me if when this started last week (10 days ago) it had been wet for afew days before and whilst I am always careful going though standing water, there had been some quite deep water going into the village and I wondered whether water ingress could be a cause.

    Will have a look at this.

    I will of course report back when I (hopefully) get a solution but in the meantime if anyone had any other suggestions will be greatfully received.
     
  17. V6Matty

    V6Matty Senior Member

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    I’m sure it’s going to be a sensor giving duff info,
     
  18. OP
    Martin Hedges

    Martin Hedges New Member

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    MY engineering background, considering the symptoms, has always pointed me to it being a sensor issue and the fact that there is one level sensor for the back I think the money is to look at that one first
     
  19. malcolm210

    malcolm210 Senior Member

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  20. OP
    Martin Hedges

    Martin Hedges New Member

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    It turns out that my car has a sensor on each rear wheel so the level sensor looks less likely. They and their wiring has been checked and seems fine so at a bit of a loss. The intermittent nature makes it very difficult to diagnose
     

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