Hi,
I wonder if anyone can help me diagnose/solve a problem I have with the REAR suspension intermittently collapsing on my 2005 W12.

It only collapses when I change suspension height settings whilst either driving, or standing, for example changing from Auto/Comfort to Dynamic, or the other way. When this happens, I pull over, switch off the car, re-start and the rear suspension pumps back up straight away and I finish my journey (staying in the same mode to prevent reoccurrence). Not wanting to risk permanent collapse, I have now stopped driving it.

It does not sag or collapse when parked. I have parked the car in various modes, including (high) 'Lift' mode with Jacking mode 'ON' for over a week, to test if the air bags have a leak, but there is no drop from any corner.

The compressor sounds fine and is not continuously pumping - so doesn't appear to be the problem(?)

The compressor does appear to 'click-in' a little more than it used to when I first bought the car 8 years ago (at 75K). It has now done 154K miles, without any issues from the air-suspension, until now.

Surprisingly, there are no suspension Fault Codes from my VCDS. I also have the Bentley manual, but could do with advice before diving in and replacing (some possibly very expensive, unnecessary) parts randomly.

Following reading many posts on this subject (virtually all relate to the Front, rather than Rear), my suspected culprits (in order of likeliness), I believe are;

1. A rubber 'o'ring seal somewhere (but where);
   1. Susp unit Inlet valve?
   2. Valve Control unit/block?
   3. Residual air valve atop one of the rear suspension units?
   4. One of the air-lines (but surely this would leak constantly whilst driving)?
2. Valve not closing correctly inside the Valve Control block?
3. A rear height sensor?

So, I would be very grateful if anyone could advise (ideally from experiencing/solving a similar/identical issue) which elements of the system are the most likely cause?
Many thanks
Malc :-)

Thanks for the speedy response and tips MP. I'm hoping the snow here will clear soon, so I can investigate.

My money is on an electronic problem. The fact that there are no error codes, despite there quite obviously being a malfunction, and a restart resolves it leads me to that conclusion. Either bad level sensors or a faulty suspension ECU.

As you have VCDS, put it to work and run an output test on the level control module. Pay particular attention to what the the readings the rear level sensors are spitting out. Are they inline with what the front ones are doing?

Thanks Dave, sounds logical, as does MP’s suggestion of a poss dodgy Relay. I’ve not used VCDS for an output test, but will try to find my way and report back when complete.
Cheers
Malc

That’s odd as most people on this board are US based where many owners (such as myself) live in way colder, way snowier climates than you will ever see in any part of the U.K. and cold temp suspension collapses aren’t a particularly known issue.