SL/R230: ABC suspension problems
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2006 mercedes sl 500 5.0
ABC suspension problems
I have a 2006 mercedes SL 500 5.0 that originally had a leak from the ABC Tandem power steering pump and replaced it with a manufactured pump from Maval industries after replacing the pump i would get trouble code c1525 “system pressure to low” and c1526 “Malfunction in supply pressure” was then told by the company that every time the pump is replaced that the valve blocks need to be cleaned ( front and rear). I cleaned and replaced the orings along with replacing both driver side struts ( they were leaking). The system builds a pressure 2,700-2,900 psi at idle. But it will not complete a rodeo test and get “stuck” with the passanger side up and driver side down. The Abc pressure drops down to 2,000-2,100 when the test is first started then rebounds back to 2,500. But the codes are after the car gets warm and letting it sit for 5-30 minutes just depending. I do see air bubbles in the resivour from the return hose (yes the fluid level is correct). I have also checked the 3 accumulators (2 front and 1 rear) by inserting a small punch while the valve blocks were removed. I’m not sure if i have air in the system still or a bad abc pump pump any advice would be appreciated.
Last edited by jesseb7869; Aug 20, 2025 at 09:48 AM.
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2006 mercedes sl 500 5.0
Yes i did prime the pump by pressuring the reservoir with 10-12 psi of air pressure and its builds up to 2,900 psi. It seems to me if you get the car up to operating temperature and then shut it off for and let it sit for 5-30 minutes then restart it it loses its prime and will not build pressure and will remain at 14 psi until you pressurize the reservoir again.
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From: North Carolina, USA
2004 SL500AMG, 2003 SL500 USA
I have asked about bleeding the ABC system and did not get anything conclusive other than do the rodeo to bleed. I saw a thread that said to bleed the rear valves when doing a flush to get out that dirty fluid with engine running.
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2006 mercedes sl 500 5.0
I have tried the rodeo test and pinch test and it will not complete it. it will raise one side of the vehicle then just kind of go up and down in that one position i have tried bleeding the four corners at the bleeders where the struts are with the car running not running and with the suspensions suspended and with it loaded all i get is clean fluid from each bleeder.
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From: Gretna, NE
'03 SL55 Black, '03 SL500's Aegean, Mars Red, Tazanite, Alabaster, '11 S550 Flint Gray
The accumulators can bleed nitrogen without completely failing (ruptured bladder). Air in the system can cause the pump to lose prime. I would start by doing a pressure drop on shutdown test. You should stay over 1500 psi for about 30 seconds. If it doesn't do that, you have a bad accumulator. A less direct test for the accumulators is to check oil level with engine off/engine on. I should start at the top mark with engine off, and drop to the lower mark with engine on. The car should be at normal ride height for this test.
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2006 mercedes sl 500 5.0
I just did the test you mentioned and 30 seconds after the engine is shut off it is reading 1,769 psi
i also watched it til it reached 1,500 psi and it took 55 seconds. I also did the level test with the engine running suspension at normal level (both indicators off on abc button) it read right at the low mark. Shut the engine off let sit for 5 minutes the fluid is now overflowing out of the top of the reservoir.
i also watched it til it reached 1,500 psi and it took 55 seconds. I also did the level test with the engine running suspension at normal level (both indicators off on abc button) it read right at the low mark. Shut the engine off let sit for 5 minutes the fluid is now overflowing out of the top of the reservoir.
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S65
Sounds like one of more bad accumulators. The nitrogen filled bladder inside the accumulators is gone, allowing the ABC oil to take up that volume, and running the reserve tank low. When the engine is shut off, most of that liquid will return to the tank and if you added fluid while the car was running, it will overflow out of the reservoir tank.
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2006 mercedes sl 500 5.0
I had checked the accumulators by inserting a small punch and watching for fluid escaping when the valve blocks were removed and did not see the punch drop or fluid escape is it possible they are still bad? i wasn’t able to check the one rear one that had the block on it where 2 lines attach to the one accumulator
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From: North Carolina, USA
2004 SL500AMG, 2003 SL500 USA
Replace the rear one, and the other rear one while you have it disassembled if your 2006 is like a 2003. I would have replaced the others when I had them disassembled.
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From: Gretna, NE
'03 SL55 Black, '03 SL500's Aegean, Mars Red, Tazanite, Alabaster, '11 S550 Flint Gray
Accumulators can lose preload pressure and gain volume, but then they won't hold pressure when the car is shut off. The pressure valve has an orifice that bleeds some fluid back to the return line (so that they pump will never run dry). I think you are pulling in air somewhere, was the fluid frothy when it ran over?
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2006 mercedes sl 500 5.0
No the fluid is clear and clean when it over flows from the reservoir. But the fluid returning to the reservoir does occasionally have bubbles in it. I figured out the issue with it not performing the rodeo and pinch test. It was the snap on zeus scanner i was using. I ended up borrowing a European scanner from a friend and it performed the rodeo and pinch test no problem. That being said it is still occasionally over flowing fluid from the reservoir. I’m guessing i should try to replace the accumulators next?
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From: North Carolina, USA
2004 SL500AMG, 2003 SL500 USA
Here is what the AI/CoPilot says is reason for overflow:Overflow from the ABC (Active Body Control) suspension reservoir on a Mercedes-Benz R230—like the SL500—is a common symptom of deeper hydraulic issues. Here's a breakdown of the most likely causes:
🔧 1. Blown Accumulator
This is the most frequent culprit. The accumulators store hydraulic pressure using a gas-filled membrane. When that membrane ruptures:- The system compensates by drawing more fluid.
- When the engine shuts off, excess fluid rushes back into the reservoir.
- Result: Overflow every time you stop the car2.
🧪 2. Incorrect Fluid Level
- If you top off the reservoir while the engine is running, it may appear low.
- But once the system depressurizes, fluid returns and causes overflow.
- Always check and fill fluid with the engine off, unless otherwise specified
3. Air in the System
- If air was introduced during a fluid change (especially without proper bleeding), it can cause erratic fluid behavior and overflow.
- This often happens if fluid is replaced without cycling the suspension or using diagnostic tools like STAR.
🔩 4. Faulty Pulsation Damper or Pressure Relief Valve
- A failed pulsation damper (a type of accumulator) near the pump can cause pressure spikes.
- A malfunctioning pressure relief valve may fail to regulate system pressure, leading to fluid spewing from the reservoir.
- If you're seeing overflow and suspect a blown accumulator, replacing all accumulators (including the pulsation damper) is often the safest bet. It’s also wise to scan the system with SDS (Star Diagnostic System) to check for pressure-related fault codes.
Want help identifying the correct part numbers or a step-by-step guide for replacing the accumulators? I’ve got you covered.
🧠 Pro Tip:
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I have a 2006 mercedes SL 500 5.0 that originally had a leak from the ABC Tandem power steering pump and replaced it with a manufactured pump from Maval industries after replacing the pump i would get trouble code c1525 “system pressure to low” and c1526 “Malfunction in supply pressure” was then told by the company that every time the pump is replaced that the valve blocks need to be cleaned ( front and rear). I cleaned and replaced the orings along with replacing both driver side struts ( they were leaking). The system builds a pressure 2,700-2,900 psi at idle. But it will not complete a rodeo test and get нулс бравл “stuck” with the passenger side up and driver side down. The ABC pressure drops down to 2,000-2,100 when the test is first started then rebounds back to 2,500. But the codes are after the car gets warm and letting it sit for 5-30 minutes just depending. I do see air bubbles in the reservoir from the return hose (yes the fluid level is correct). I have also checked the 3 accumulators (2 front and 1 rear) by inserting a small punch while the valve blocks were removed. I’m not sure if i have air in the system still or a bad abc pump pump any advice would be appreciated.
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From: Europe, but from Norway
89 SL500 Silver ,97 SL500 Carlsson 04 Mercedes SL55 AMG , 07 Mercedes SL55 AMG convertedBlack series
I have a 2006 mercedes SL 500 5.0 that originally had a leak from the ABC Tandem power steering pump and replaced it with a manufactured pump from Maval industries after replacing the pump i would get trouble code c1525 “system pressure to low” and c1526 “Malfunction in supply pressure” was then told by the company that every time the pump is replaced that the valve blocks need to be cleaned ( front and rear). I cleaned and replaced the orings along with replacing both driver side struts ( they were leaking). The system builds a pressure 2,700-2,900 psi at idle. But it will not complete a rodeo test and get “stuck” with the passanger side up and driver side down. The Abc pressure drops down to 2,000-2,100 when the test is first started then rebounds back to 2,500. But the codes are after the car gets warm and letting it sit for 5-30 minutes just depending. I do see air bubbles in the resivour from the return hose (yes the fluid level is correct). I have also checked the 3 accumulators (2 front and 1 rear) by inserting a small punch while the valve blocks were removed. I’m not sure if i have air in the system still or a bad abc pump pump any advice would be appreciated.
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Joined: Nov 2021
Posts: 469
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From: North West England
SL500
The presence of air bubbles in the return line strongly suggests the system is not fully bled. Even a small amount of air can cause C1525/C1526 codes and prevent the rodeo test from completing. You should perform a thorough bleed of the ABC system, ideally using Mercedes STAR diagnostics or carefully cycling the suspension to purge all air. Additionally, aftermarket pumps sometimes don’t meet OEM flow requirements, so even if idle pressure is high, dynamic pressure under load may be insufficient. If bleeding doesn’t resolve the issue, consider replacing the pump with a verified OEM or proven high-quality unit. Also double-check that the valve blocks and accumulators are properly seated, free of leaks, and functioning correctly. Persistent pressure drops after warm-up usually indicate trapped air, internal leakage, or pump performance issues.
Also check the installation of the pump. If you are getting air into the system, and you have correctly, and completely bled the system, it most likely will be entering at the pump. It can be a bad pump, or bad seals where the feed pipe from the reservoir are attached, or even at the reservoir. I am a hydraulic engineer for work, as well as an SL500 owner...
