AthlonX

Hi All, if anyone has had this particular issues you can please advise. I have replaced both rear height sensors, 1 had seized. Also have had the hydraulic fluid changed. What I have noticed is all works fine but if you sit and watch the car ticking over..ever so slowly the drivers corner slowly lowers on its own as if leaking. If it is raised up, it remains up and does not move at all, even if turned off. When driving the car I have stopped and checked it.. always ok. However, if sat in traffic for a few minutes not moving suddenly the drivers side will just drop. I have to pump up to high setting and then back down to rectify it. Dont care what it costs just want to change the failing part. No ABC warnings or errors on the dash or on reading the codes.

Many Thanks, someone must have had this exact situation..

Plutoe

"Don't care what it costs" =get a good chassis scan to determine the real problem, clear the faults and replace the faulty component!

AthlonX

Perhaps I have had a little more experience than yourself with so called experts that on the whole look at a computer screen and replace half of the car.. inevitable sometimes clearing the fault... This is a pointless comment and of no use to anyone. Do you just browse the forums looking for something to write. If you read the post.. there are no codes, it has been read...several times... I'm sure it says that.. yup it does.. no errors in codes..

kbob999

I'll throw you a bone. It may not be the issue, but you can look here.
Do you have an SDS? You state no codes, but I don't know if you are looking at a simple OBD2 adapter, or the SDS.

There are height readings in the SDS that can be read from the struts. It sounds like yours are off, reading poorly, or not calibrated right. If you have an SDS, go look for the Romess readings, or whatever they are called, in the SDS. See if they change when you cycle the height switch. If they don't, or they have a bad connection, it could cause this issue. Also check that the links are correctly installed on each side of the suspension.

Report back with your findings.

AthlonX

Thank you for this kbob, The garage read the codes. I have had no trouble with the suspension other than an ABC light 3 years ago that turned out to be the front strut ball joint. Since having them rebuilt by the same garage its been perfect..untill now. What is strange is it only does it sitting still, when moving it is sound. Got me thinking some valves shut when its not moving and they are leaking perhaps..the rear valve block maybe.. but I am having trouble finding a full description of how it actually operates. The drop when sitting still for a few minutes is dramatic.. fully drops almost instantly on 1 corner in a few seconds.

kbob999

Here's my logic. I believe there are 2 things that can cause this: the fluid is leaking out; or the fluid is being controlled to drain out. No fluid movement...no drop.

When was the ABC fluid and filter last changed? Is the fluid green, or dark? If dark, change it.
Can we eliminate the valve block as the culprit? Does the valve leak, and at idle the engine pump can't provide enough volume to overcome the leak? That would be a massive valve leak.

If the valve block is good, then it must be the controls. This could be the height controller and linkage, the sensor in the shock, or the wiring having a bad connection. The movement of the car may give enough vibration to keep a wire connected, or a sensor out of a bad spot.

This is why having the readings from these devices above would pinpoint the issue. This requires the SDS. Otherwise, you are throwing parts at the car with no idea what is wrong.

AthlonX

Fluid was changed just 3 weeks ago and the filter, genuine merc stuff. Also at the same time the height sensor was changed. I have today watched closely. When idling, ever so ever so slowly the car is sinking on the same corner. You can't see it, it's so slow but it is dropping continuously. I measured height to arch and is defo dropping slowly. Sometimes its sudden as explained. Strangely when driving, I have stopped jumped out and inspected.. all is ok..its like when its idling and not moving, something else comes into play which is why I am thinking the valve block shuts off or something when the car is not moving. I can get it on SDS but not for at least 2 weeks due to working away. I will et you know what they find.

carguyshu

I've had the problem. the issue is fluid leaking past the orings in the valve block on the locking valve. the valve block needs rebuilt with new orings or replaced. what happens is the locking valve is closed and supposed to prevent any fluid from going into the strut, but since it is leaking the fluid continues to go in. Eventually the car gets too high and the car recognizes this and drops the car down rapidly. this is exactly what is happening in your case.

as an FYI- how the valve blocks work is there are 2 valves for each strut (total of 4 valves per block). one (the tall ones) lock and prevent fluid from going in or out of the strut. when you are stopped this one activates and stops fluid from going in/out. the other valve opens or closes and either lets fluid in or out. When you are driving this is continuously acting and thus you have no idea if the orings on it or bad or not as the car is constantly self adjusting fluid in or out of each strut.

carguyshu

also, here's a good writeup on ABC. the prices are a bit off as the blog is old, but it should help you get a better understanding of the system.

http://mercedes-abc-drive-carefully.blogspot.com/

AthlonX

That totally makes sense (apart from I would expect an over pressure error or some other code to spring up and be logged - but often the diagnostics are not perfect), I had a feeling there was something different going on when driving to be stationary. I will look into replacing the valve block. Its 14 yrs old so it is to be expected I guess from what i read. oddly though as mentioned the shock does not go up at all from normal, just slowly drops or drops suddenly, but the locking valve is likely the cause as you explained.

ItalianJoe1

There is a bulletin for the early cars about sudden level adjustments when parked. It's normal, a function of the programming in the ABC controller. If there are no faults, and all you get is that feeling of a sudden drop (it rises slowly, you don't normally notice when in the car), the only resolution is replacing the ABC module with a newer one that uses different logic when stopped to prevent that sudden movement. I'll try to find the bulletin at work tomorrow. Both of my CL's have done this, I though it was an issue, but it's just the way they are.

What year is your SL?

AthlonX

Mines a 2003, Only dropping on drivers side. My understanding about this bulletin was it was not shock specific, which mine is.. Be interested to read it however if possible. Thanks. Ordered a valve block rebuild, will tackle it in the next 3 weeks when i get home. Looks pretty straight forward to do. I would have considered a used 1 but the prices of these things are crazy and you are likely buying a worn out unit anyways. If its going to be rebuilt, I would feel better doing it myself.

carguyshu

Rebuilding the block is easier than removing it. A set of dental picks to remove the rings makes it super easy. The taller valves (the locking ones) you spin 90 dog to remove & the other valves 45.

Make sure you mark the lines & electrical connectors when removing the block. I accidentally swapped the pressure & return lines on the distribution block above the valve block & let's just say that was an expensive lesson.