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Discussion Starter #1
Hi, I recently have had the high pressure hose of my 2003 SL500 replaced (costed $2000 parts and labor). However, after replacing the hose, the car is now acting weird. It drives normal at the beginning. But after driving for about 30 minutes, the white ABC visit workshop warning will randomly come out on the dash and the car will raise itself up to the highest. You will feel very bumpy like hitting a rock on the road. Only when I stop the car and turn the car off, all four corners will sag down right away back to normal. But if I drive the car again, same thing will happen again after like 5-10 minutes driving. I didn't notice anything specially caused this as it came out pretty randomly. Only thing I noticed was that it didn't happen when the car is cold. Only after I drive the car up to the normal operating temperature, this funny thing will start to happen.

I had the car checked back by the indy who did the hose job for me. He used the techbook read the system, showing the right pressure of the system, and nothing wrong with all sensors and the ABC pump. and obviously he had no clue how this happens.

He asked me to bring the car to a Mercedes dealer. But before spend $$$ with the dealer, I'd like to see if anyone in this group had the similar experience like this before and how you solved it.

Any suggestions/advice of how/where to diagnosis this problem are highly appreciated!
 

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It sounds like the ABC computer directs all four control valves to raise the car all the way up, and then stops making any adjustments to allow fluid in/out of the struts. When the adjustments stop, the car would have terrible ride quality.

My theory is the car thinks it’s much lower than it actually is and is trying to achieve the correct ride height but can’t because the calibration is off.

I think I read about something similar to this in another thread somewhere. Is there a chance your mechanic started the car while it was still up on the lift after performing the repair? From what I remember reading, this confused the ABC computer and caused ride height problems.
 

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Discussion Starter #5
Im done with that mechanic and have my car at home now (in another city). But I remember when I had the car at the mechanic's place, he did put the car up on the lift and started the diagnosis, but just couldn't figured out what the cause was, as it happens quite randomly. Even with all suspensions up at highest, his computer didn't show any wrong code.

Im kind of thinking the ABC computer. As it only happens when the car warmed up and when I drive locally. It never happens if I drive on the highway straight after I start the car. Could it be some kind of heating related problem so the ABC computer decide to keep raising up all four suspensions till the engine (ABC pump) shuts off?
 

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Or...what if you are having a control valve problem (bad o-rings?) and fluid is getting pushed past the valve into the strut. The strut fills up until it’s completely full...causing high height and a bad ride (because the computer cannot let fluid in/out of the strut at this point because pressure is forcing fluid into the strut nonstop). This causes a temporary pressure drop in the system (white message). Then when you shut the car off (system depressurizes) the struts lower while fluid can still bypass the compromised control valves until the lock valves ultimately stop the flow of fluid, and the car rests at a normal level....

I just had to send both of my valve blocks off to get rebuilt because I ruined them when doing a fluid flush. In my case, the lock valve o-rings presumably failed and the car was sagging. But the failure was inconsistent, sometimes the valves could hold fluid and sometimes not. Given the randomness, I wonder if you have something similar going on, just on the control valve side instead.
 

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Discussion Starter #7
That sounds logically possible. I've already ordered two used control valve units (one front and one rear) and was thinking to give it a try. The question I had on this was that if it was one of the control valves or both leaking, when the suspension height went up, would the height sensors tell the ABC computer to open up the return valves to get the fluid returned till the struts back to the correct height? or there are simply no so-called return valves that control the fluid return?
 

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There is only one control valve for each strut. The valve has three positions: fluid in, fluid out, closed. When the valve is in the “fluid out” position, pump pressure is just taken off the strut for a split second and the weight of the car forces fluid out of the strut back into the system. If fluid is getting pushed past that valve, it’s not possible to ever take pressure off the strut and I would think it would still be filling up the strut even if the valve was in the “fluid out” position.
 

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Discussion Starter #9
If this is the case, what are the chances that all four control valves are leaking and consistently "fluid in" to the struts?
 

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That would be crazy bad luck haha.

I wonder if only one is bad and the car ultimately decides to just raise the others to keep the car level. I’m not sure how the computer prioritizes ride height vs level ride.
 

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If this theory is correct, the strut with the bad control valve should never drop during rodeo as it would be impossible to get fluid out of the strut. You would have to do the rodeo when everything was heated up already and the failure condition was currently happening.
 

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Discussion Starter #12
Yeah, but thank you for all the information. I will definitely check the control valves once I receive the orders and let you know.

Wondering if you have any source that talks about how this ABC system works in details? I really want to understand the design and mechanisms behind.
 

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It should be working now.

You really should have the shop try a rodeo after the car has raised itself up again and see if there is a corner that isn’t dropping like it’s supposed to.
 

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Discussion Starter #16
ok. Thanks.

I may buy a STAR kit and do the rodeo myself, as the shop charges too much for working on this ABC system.

Thanks,
 
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