R230 - ABC Fluid level while engine running

[Koopz]

Just before Christmas I got the dreaded red ABC warning. Suspension went very floaty and the button to raise and lower stopped working. Got the car home and plugged it into SDS and had System Pressure Too Low and Malfunction in Pressure Supply faults. Pressure was reading around 110-115 bar (I believe it should be about 180). Checked the fluid level and it was low, so I ordered some fluid and waited. Got it topped up yesterday morning to the correct level and straight away the warnings went away and the button to raise the suspension was working again. Checked the level again this morning and it's still in the same place, so if it is leaking somewhere it's not a catastrophic leak. I haven't checked the pressure reading yet, and the car is not currently being driven.

The thing that is really confusing me though is that when I check the fluid level on the dipstick with the engine off, it's in the right place (on the high mark). But when the engine is running it's way too low - right at the bottom of the dipstick. Turn the engine off and wait for half hour before measuring again - back to the high mark. Where could the fluid be going while the engine is running? Has anyone experienced this before?

 

[Binnedit]

Hi

i'm no ABC expert, but have done some reading up on the system as I'm awaiting delivery of my new CL.

Sounds like a Accumulator has blown, and taking more fluid to fill to capacity when the engine is running, and returning to the reservoir as normal once the system is switched off.

I'm sure others with more knowledge will be along to confirm or deny.

 

[Koopz]

Thanks for the reply. From what I've read that's probably one of the least expensive things to replace so fingers crossed that's what it is!

 

[Timeandleisure]

Hi, a bit of a read but fascinating and helped me persuade the dealerships to look into other solutions besides the usual suspects...

ABC System

Welcome to my guide for the Mercedes Active Body Control (ABC) Suspension System. In July of 2014, I purchased a used 2003 Mercedes ...

mercedes-abc-drive-carefully.blogspot.com

 

[Koopz]

Hmm. Reading through that it seems to be saying if it was a blown accumulator I'd have the opposite problem and there would be too much fluid in the reservoir when the engine is running. Fantastic info though thanks

 

[LostKiwi]

From the article linked above:

Observing the dipstick levels. There are two notches on the dipstick. The lower one is when the engine is running, the upper one for when the system is off and fully depressurized. If your fluid levels are set correctly for when the car is shut off(the higher mark), and then you start the car and don't see the fluid level drop to at least the lower mark, then there is likely a blown accumulator(s). On my 2003 SL500 with 4 fresh accumulators, the level drops from the top notch to about 1+1/3 the distance between the two notches. Each of the two main accumulators account for about 1/3 of the level drop. The pulsation dampener and return accumulator are smaller and together make up the last 1/3.


This makes sense to me as without pressure in the system the accumulators will push fluid back into the reservoir. Then when the engine starts pressure will push fluid into the accumulators.

 

[Koopz]

I agree that makes sense. What confused me was he seemed to be saying if an accumulator is blown the level won't drop.
"If your fluid levels are set correctly for when the car is shut off(the higher mark), and then you start the car and don't see the fluid level drop to at least the lower mark, then there is likely a blown accumulator(s)"

Regardless, it seems to be a relatively easy thing to get to and check, plus the car is coming up to 20 years old with 63k on the clock so its probably smart to just get them replaced anyway!

 

[LostKiwi]

An accumulator is just a sealed ball split by a rubber diaphragm. One side of the diaphragm is sealed and under permanent pressure.
The other side is connected to the rest of the system through the high pressure line.
When the pressure in the hydraulics drops the high pressure nitrogen on the other side of the diaphragm will push oil back to the reservoir. Therefore if the accumulator diaphragm fails the level will drop initially but then remain constant as the diaphragm is no longer able to force fluid back into the system.

 

[Koopz]

I think the way to go is to replace all of the accumulators and while that's happening rebuild the front valve block as the front passenger side drops occasionally. It's all something I'd try to do myself but I don't have a garage and not sure it's something I could do on the drive (especially in this weather!) So I'll call a couple of specialists and see what they can do. Might even get a quote off Mercedes for a laugh

 

[LostKiwi]

Personally if its working now and the level is correct and behaving as expected I'd leave it alone. Read through that document and see if you have any issues before tinkering as it can be an expensive slippery slope.

Don't let Mercedes anywhere near it!

 

[Koopz]

It works but as I say the fluid in the reservoir is very low while the engine is running, so I'd be worried about damaging the pump

 

[LostKiwi]

Engine off is it on the correct level?

If so engine on is it above minimum?
If so leave it alone.

Note there are two sides to the dipstick. One side engine on (motor an), other side engine off (motor aus)

 

[Koopz]

Engine off its at the correct level. Engine on its pretty much at the bottom of the dipstick, way below minimum

 

[Flyinspanner]

Engine off its at the correct level. Engine on its pretty much at the bottom of the dipstick, way below minimum

Top it to above minimum engine running.
I’d suspect one of the accumulators, £170ish - when you get it fitted get the fluid changed, and the 3micron filter changed.

 

[Koopz]

If I stick in a litre or so to get it above minimum while running will it overflow once the engine is off?

 

[Koopz]

Also I had the fluid and filter changed a couple of months ago, would it still need a flush after changing the accumulators?

 

[Koopz]

Thanks for all the replies btw I appreciate all the help

 

[Flyinspanner]

If it is an accumulator which has failed, the rubber diaphragm will have failed, this will allow tiny bits of rubber into the fluid, and potentially corrosion particles from the previously “dry” side of the sphere.
Those particles can damage seals in the valve blocks.

 

[Koopz]

Would need flushed then, thanks. I've ordered another litre of fluid that will arrive Sunday, will try and add a bit more while the engine is running but I don't know how much I'll be able to get in without it overflowing when the engine is off and it all comes back into the reservoir

 

[LostKiwi]

I doubt you have a failed accumulator - the symptoms are all wrong.