I was driving on a road that I know doesn't have bumps and is fairly well-paved (considering it's in Los Angeles), and my car started bouncing a lot, which is very odd. Then I look down at the two displays, and the one on the left reads 'ABC'. No warning or anything labeled in red, just the simple ABC. So I switched the reading back to its original position, and it stopped. Now, no more than a year ago, I had the filter changed, emptied the old fluid, and replaced it with fresh fluid. I wasn't having any issues, but I thought it might be a good idea to perform that maintenance. So, is the ABC system about to go south on me?

Thank you.

 

You probably had an intermittent sensor fault that caused it to go into the fully raised passive limp mode. I wouldn’t be too concerned unless it starts to happen with some frequency.

 

Hmm...I never heard of such a thing. My two most significant questions would be these. If, indeed, and hopefully, it's just an intermittent sensor fault, what would cause that fault? In other words, would I need to replace that sensor? Second. If it's an ABC issue, I'm guessing it would be more advantageous to sell the car instead of replacing the ABC system itself.

 

I suspect the ABC system compares the position of the mechanical height sensors to the plunger travel in each shock. A discrepancy might result in an ABC message and limp mode. There are also 8 (or more?) accelerometer sensors which allow the system to keep the car level under cornering, braking and acceleration.
IMHO, If the ABC light turned on after hitting a pothole, I would first check the mechanical height sensors. However since the car started bouncing on a flat road, I would suspect an accelerometer or a corroded connection to it. Just my opinion.

 

The worst case is probably a pump getting weak, but there are numerous other faults that will put it into limp mode. It will throw a code in the ABC module, so have the codes read and go from there.

 

I'm having the car checked out today. I'll get back with the results.

Thank you.

 

Hmm...I never heard of such a thing. My two most significant questions would be these. If, indeed, and hopefully, it's just an intermittent sensor fault.
I have. Happened two or three times at random in ten years - switch the car off and on again to clear. Not sure it's a fault - just a glitch in the system. You have the 'Tuna Boat Ride', as it's called around here, which seems to be a bit of a random event.

 

Just a short update. The pump is functioning correctly, but it's losing pressure through the lines, and the location of the issue is currently unknown. Additionally, it appears to have lost fluid, yet there is no leakage.

 

How did you measure the pressure - on either a scanner or STAR? It should show the pressure around 190, then when you switch off should diminish.
How do you know it's losing pressure?

Additionally, it appears to have lost fluid, yet there is no leakage.
If you have lost fluid, then there is a leakage - that's incontrovertible. You just need to find the leak. I'm assuming you're going by the level in the tank.
Now a leak doesn't have to mean fluid on the ground. There are two likely sources for fluid loss. The accumulators can blow then fill with fluid, but in this case the level will drop and stay low. The other source is from the pump area where fluid can travel a long way on the under-body cladding on the sides of the car and pool there. Slip one off and inspect.

 

My mechanic was measuring the pressure using a scanner. What type of scanner he was using, I have no idea. The pressure was fluctuating at 148, then dropping to 144, then 140, and so on. Since there is a pressure leak, reaching that 190 number would be out of the question. What I dislike, and why I'm not driving it until I can get it back in the shop, is that when I start the car, I can hear a rattling noise from the engine that then travels to the rear of the car, culminating in a loud bang. That happens on either the driver's or the passenger's side.

 

No idea about the travelling bang, but this sounds, at least, like the pump has lost pressure. Has it been replaced? They wear out and lose pressure.

 

The pump is in excellent condition. It's losing pressure somewhere in the lines that the pump provides. I'll get back to you all when I have more detailed info.

 

*Update. So, when we checked all the lines for the fluid leak in the ABC unit, none could be found. Once the reservoir was filled again, the ABC Malfunction would no longer appear, and everything was running smoothly once again. Except I still have some concerns. When I originally had the ABC system check, replaced the filter, drained the old fluid, and replaced it with new fluid, did they not fill it up to the level it needs to be at? The reason is that I have never found any leaks from my car since I have owned it. And I don't think that the ABC fluid can evaporate. Also, after we added the fluid, I still occasionally get a "Bang" sound from the rear driver's or passenger's side. I have had that issue since I bought the car two years ago. I was told it was because of the buildup in pressure in the ABC system that can cause that "Bang" issue, and that it's common with older SLs. Frankly, I think that Bang sound can't be good for the car, but I'm told it's not an issue. Can this be true?

Thank you all once again.

 

Sounds like the tank was a little low. Now just monitor the level and see how you go. Is it losing fluid now? That's the question.

I still occasionally get a "Bang" sound from the rear driver's or passenger's side
Probably rear subframe bushes. How loud is it?

 

Or.... the rear Accumulator is starting to lose pressure. A telltale sign is slightly lower line pressure, and overall fluid levels will dip.
Here's the fun part. To begin with, only after warmup does the ABC tank level drop. Shut it off and the Accumulator bladder begins to push back fluid into the reservoir.

Due to the bladder inside the Accumulator not holding pressure the volume is displaced with ABC fluid and the car doesn't react well to faster compression because you're reaching closer to a solid ( no Accumulator pressure to cushion the shock impact.
Good news is; diagnosing the loss of Accumulator pressure before you blow a line and/ or ruin a Valve block.
Good Luck
Hary

 

*Update. When I took the car in, it displayed two codes—525F and 5262. After refilling the reservoir and rerunning the scan, those codes no longer appeared. Note to Harry. Your correct. The assumption thus far is that the fluid could be leaking in one or all three accumulators, which would explain why we don't see any leakage at all. This means that at some point in the near future, I'll need to replace all three, which will cost approximately $2,100.00. Presently, when I start up the car, you can hear the buildup of pressure, which is not pleasant. But the car is running great again, and I'm having fun while driving. But here's the long-term question. The SL is a 2007 model with just under 74,000 miles. So, I'm thinking that I've already paid well over $ 10,000 over the two years since I purchased this car. As a result, I'm seriously considering selling it and possibly buying a 1960s classic. Not an MBZ, but more in the line of a 1968 MGB or a 1972 TR6. Or maybe a 1994 Ford Bronco or a Toyota Land Cruiser 60 series. I can't keep reaching into my pocket and pulling out thousands of dollars every time I visit my mechanic.

 

You were warned

 

By whom?

 

When do you get the "bang" sound?

 

$2100 sounds high!

2x Accumulators cost me $300
1x Pulsation Dampner was $150

Labor-$550 and that included an overpriced can of abc fluid from the dealer.

All in around $900 to keep the car going for a decade.

I think prices went up in 2024-2025 as well.

p.s def should not be any banging sound.

 

I don't see how a failed accumulator would give you low ABC pressure. Sure it would take a few extra seconds to fill, but once full, the pump should be able to raise full pressure.
Without a leak, I would first suspect the pressure regulator valve located near the pulsation dampener. IIRC there was another thread here a few months ago where the OP replaced the pressure regulator valve with one from ebay and it solved his low pressure problem.
Theoretically a valve block could leak fluid resulting in low pressure, but I haven't (yet) taken one apart enough to see how that could happen.

Yes, the $2100 sounds high, although $550 labor now sounds low for a likely 4 - 5 hour job.

IMHO, unless you are comfortable doing all the work yourself, find an independent mechanic who is familiar with these cars. Buy new parts from online courses, which typically are dealerships with an online parts department. And ebay is your friend.

 

*Gaazmon. I have had that "Bang" on and off since I purchased the car, which will be two years as of this August. *Mrvedit. I didn't say anything about a failed accumulator. What I stated was that there is a leak, and since we can't see said leak on the ground or in the lines, it might be leaking into the accumulators. And since the reservoir was refilled, I have not experienced the ABC malfunction. When I retested, the two codes I mentioned were no longer showing up. But you know as well as I that sooner or later, I'll need to replace the two accumulators and pulsation dampener.

 

When do you get the "bang" sound? - as in, under what circumstances? Probably subframe bushes, if when backing up then moving forward you're hearing it.

 

When I do get the bang, it's right after a cold start. Meaning, when I get up in the morning, while the car has been sitting for 6-8 hours, I will get that bang. Not all the time, mind you, but it does happen from time to time.

 

**UPDATE: So this morning (06/29 @ 0532) I'm driving on the FWY and hit some deep dips, and I swear on the first one the car bottomed out, that both the left that reads out ABC and the right that reads out Malfunction went RED but as soon as it turned red it turned back to regular reading. This happened a total of three to four times over a thirty-mile stretch, hitting the deep dips in the FWY. As soon as I got off the freeway and started driving on city streets, it never turned red. And here's the odd part. One would think that when both went red, it would revert to the standard color, displaying ABC on the left and 'Malfunction' on the right. However, it didn't happen as it did before, without the left or right going red. So, with that said, I'm guessing I'll be heading back to my mechanic on Monday and spending a tad bit north of 2K. But hey, let's look at the silver lining here. I have replaced most, if not ALL, major parts on the car, except for the transmission or engine. Oh, the joys of owning an MBZ.....