I've got a left rear shock that quickly jerks up and down several times before shutting down to ABC fault in red on the dash. Turn the car off and goes back to normal. Can drive 20 minutes, nothing. Sits at a stoplight, and like a low rider with only one working hydraulic, the left rear rises up and down really fast!
Pump was replaced and holds steady at 190 PSI During Rodeo dips to 170 but recovers fast.
I removed and inspected large accumulators at the front and back and the membrane is intact. Have not replaced the small ones. Ride is nice and not harsh.
No leaks under the car. Fluid is clear green since I replaced it. New filter. Rodeo several times purging air bubbles. One shock shows faint weeping but can't see a "leak"
In the past, an updated valve block, the non serviceable type, was installed. This one has the solenoids that can't be twisted out. I do have two old serviceable ones on standby if needed.

Right now I'm leaving towards the issue being the level sensor, or the height sensor that is built in to the shock. I've considered the issue lying in the valve block, may the plunger orings not sealing, but I would think I get sag after a week or two of sitting....I dont.

Anyone experience the one corner trying to dance with the lowriders! ???

 

Sounds like a ride height sensor, very possible you have one not sending the correct voltage to the computer and causing issues. I would work in this sequence:

Find a used (Rear L or R) ride height sensor on Ebay or locally and swap out. Clear all codes with a quality certified shop scanner, do a full clear on anything that comes up. Hook up a volt meter to your battery and make sure your battery is fully charged. I would leave it on a tender over night before all of this to make 100% sure. Weird things can happen with these cars with a drained battery. Replace the ride height sensor and see what happens. If nothing happens and the car stays normal you've fixed that issue.

Chances are this problem isn't related to the pump, accumulators, strut or a valve block, however I would absolutely replace everything i just mentioned. Theres no way to "Test" an accumulator that i'm aware of and they all need to be replaced after X Mileage or X Years. If they haven't been replaced with documentation i would do it sooner then later, because you WILL blow a line or have other issues later down the road directly related to the Accumulators. Do it and its done. 2ndly, I would remove the "Non-servicable" valve block as that just sounds like an issue. Buy two factory valve blocks for both the front and rear and rebuild them on the bench. The rebuild kits are cheap and its not incredibly difficult to tackle. The kits now come with White Plastic or Teflon rings which don't wear out as easily. I would recommend those. Make sure you don't pinch them when you're putting the Valves back in the block. I pinched one of mine and i believe its a possibility as to why my driver side front strut drops down as well, but honestly i'm not sure. Just take your time and don't force anything and you'll be fine.

Theres a program on a scanner you can pull up to monitor proper voltage coming from the ride height sensors while the car is on and also in rodeo mode i believe. If you can find that, I would do a rodeo and keep an eye on each corner as it relates to voltage. However, as i mentioned swapping out the RHS for a used one should give you your answer.

- Joe

 

OP do you have Xentry? Smrat move being plug it into MB's very own system and watch 'Actual values' in real time to see what the car sees. It should have codes in it to lead you to a realistic diagnosis.

 

thank you for the detailed response. The accumulators were checked by probing the membrane to see if it was intact. Maybe there’s an accumulators can be older and not working properly if the membrane is still good, but maybe it becomes too firm?

I wanted to replace the right height center, but was told I would have to have a special factory computer to recalibrate the right height afterward. I have a basic Icar soft scanner. It can do the rodeo and the monitoring of the voltage from the sensor.

I already rebuild one of the valve blocks with a new kit and will likely swap out the updated version because all of the ports look identical.

I am tempted just to call a local shop with factory computer to see if they could pinpoint either the external sensor or the internal sensor in the strut as being the problem.