Turboaction

I'm a relatively new owner of an 03' S600. Looking through the records of this car, the ABC pump was replaced about 40K miles ago due to a noise complaint.

Recently, I've been getting an assortment of ABS warnings, white, blue, and red. I've hooked up the STAR diagnostics to the car and the ABS pressure is sometimes over 100 bar, and sometimes it's 2 bar. It's not a sensor fault, as when the pressure is 2 bar the diagnostic test is unable to lift the car.

The system has been full of fluid since I've owned the car and there isn't any metal in the fluid. I tested the flow control valve on the ABC pump and it appears to cycle normally. I've also checked the wiring from the flow control valve to the ECU and it looks ok.

Has anyone had an ABC ECU go bad? I don't see how a mechanical pump can change operation randomly unless the flow control valve isn't opening (it's normally closed when no current is applied).

Let me know if any of you have experienced anything like this. If I can't figure it out, I guess I'll pick up a used ABC controller and double check the wiring. This isn't my primary vehicle, so I have some time to sort this out.

Welwynnick

What are the stored faults recorded on STAR?

Nick

Turboaction

There were two codes for low supply pressure (and later 4 codes for critical ride height). I cleared the codes and the system started back up, pressure about 80 bar during a brief rodeo actuation test at 1500 rpm. I don't have the cooling fan installed right now, so I only ran the engine for about 5 minutes.

The car didn't have any ride height/sagging issues. The ABC faults showed up while the car was parked at my house as I troubleshot a bad intercooler circulation pump. I don't know how the system went from working great to not at all without even driving the car around (besides around the property).

I'll post some more detailed symptoms once I have a bit more time to document everything

mrbobby

I suspect the pump. I believe there is an electrical sensor in the pump itself. On my S 55 I had a similar issue and had to change the pump a second time. I have a brand new pump here with that defective electrical component.

Turboaction

Ok, the saga continues!

I started up the car with the diagnostics hooked up, 175 bar system pressure. I immediately raised the car to the normal ride height. This was successful, but I noticed the system pressure was slowly dropping.

I then activated the rodeo test and the pressure continued to fall to about 60 bar after about 1-2 minutes, then it shut off. I tried to re-run the ride height actuation and it failed to run, giving a communication error. I then ran the suction restrictor valve actuation test and the pressure did not change whether the valve was wide open or closed. The pressure continued to slowly decrease, eventually reducing to about 40 bar.

I turned off the car and re-started the engine in an attempt to run the ride height actuation test. By this time, the system pressure was only 2 bar and once again, the ride height actuation test failed. There are no external fluid leaks.

The active codes are "pressure supply malfunction" and "system pressure too low". Is it normal for a dying pump to have good pressure when cold, then drop below a critical pressure after running for a while? I can't imagine the fluid viscosity changes enough to go from building 175 bar at 10C, and essentially no pressure when warmed up. Maybe the springs in the pump are broken and the pumping elements stick as they warm up?

Anyway, give me your ideas. I'll order a known working pump and see if the symptoms change. If things start working, I can get a new pump on order.

Turboaction

Ok guys, I don't think my issue is the pump, but rather the pressure regulator block, and this is why:

I started the car cold, hooked up Xentry, and began the ABC pressure sensor test. This test reads the sensor for about 10 minutes.

The first time I ran this test the pressure was 175 bar at idle, with about 5 bar oscillations for the first four minutes or so, then it was nice and steady at 175 bar. At the eight minute mark I revved up the engine to about 2500 rpm to see if I could get a pressure spike, and sure enough, it went up to 180 bar, then began to rapidly fall to about 80 bar until the test ended.

I re-started the test and the pressure started at about 60 bar and slowly declined down to 5 bar when the test terminated.

I tried to raise the car and the car wouldn't raise. I cleared the codes, shut off the engine, then re-started and checked the pressure. Still 4 bar. I repeated this process a couple times and the pressure never increased.

Each time I start the car after it has been sitting a while, the pressure is fine and I can do actuations. The problem seems to show up once I rev up the engine (which most likely is increasing pump flow and opening the regulator). This would also explain why the system worked perfectly one day, and not at all the next day. It would also help explain why I get no strange pump noises.

Anyway, let me know what you guys think. Before I go to bed tonight I'm going to start it back up and see if it will build pressure again. The plan is to buy a used valve block, then disassemble it, replace the O-rings, and install it on the car. I'll disassemble mine, and if it looks rebuildable I'll fix it and keep it as a spare.

Let me know if you guys have ever heard of symptoms like this. It really does seem like a stuck regulator, as the pressure decay from 175 bar to 80 bar was very non-linear, then started to become more linear as the pressure came closer to zero. This is very similar to a pressure decay curve with a fixed orifice.

In my professional experience, fluid regulators tend to fail in the open position, and they tend to like to collect debris (which causes the failure). Are there particular components in the system besides the pump that are notorious for shedding debris? When you guys say to replace the O-rings, are you talking about the seals in the valve blocks?

I realize I'm a complete noob, but I promise, I'm a well educated noob. The more I work with this system the less intimidating it is.

Welwynnick

Yes, don't be afraid of ABC. Its only nuts and bolts, oil and rubber.

Your reasoning sounds very reasonable.

If you can, I'd be tempted to simply remove and dismantle the pressure regulator, and see if there's any damage or debris in there. New parts are either extortionate or unobtainable.

Good luck

Nick

Turboaction

I luckily found a whole regulator/damper/pressure sensor for $125, so I picked it up for spare parts. If I have time tomorrow, I will take my regulator apart and see what's going on inside. The original goal was to try to take off the original valve assembly and install an inspected one quickly to help avoid a mess of fluid loss. I'm trying to avoid removing and adding fluid more than necessary to minimize the chances of contamination. Of course, a flush will be required once I get everything back together. The old fluid was more of a brown color than green, so it really needed to be changed anyway. I think both the ABC and power steering systems will thank me for the fresh fluids.

Anyway, I'll post pictures of whatever I find in order to better help others diagnose their systems. The Xentry diagnostics really doesn't even consider the regulation circuit as a potential cause of low pressure.

Turboaction

Well, tonight I installed the new intercooler circulation pump and disassembled the old one. Needless to say, I could have repaired my old circulation pump for about $4. I may offer a rebuilding service down the road if there's interest. I'll locate the parts needed once I get some other things taken care of around here. If anyone cares, I can make a write-up for how to repair the pump. Of course, I imagine on this forum most people aren't interested in repairing something that only costs $100 new.

Welwynnick

Were the commutator brushes worn out?

All the best pumps have replaceable brushes or electronic commutators.

Nick

Turboaction

Exactly, the brushes were simply worn out. I haven't measured them yet, but it should be a simple repair. I think the hardest part will be re-assembling the motor, as it may be challenging to get it back together without removing the impeller from the pump.

Turboaction

I thought I'd give you guys an update. I cleaned the used regulator/damper valve block and installed it on the S600 tonight. The system now holds pressure and the ABC system seems to work normally. I'm going to flush plenty of clean Pentosin through the system to help improve the quality of the fluid and send it back into service.

So, if the pump sometimes builds pressure, but other times doesn't build pressure. replace the regulator block.

I'd love it if somebody could explain what the components inside the block do. There appears to be a check valve in the high pressure banjo bolt, a high pressure regulator, and some other valve. Any insight into exactly how these components function would be helpful.

ibeforreal

When you have time write up your fix if it's not a problem. Pictures also help.

Turboaction

Ok, so the saga continues. I think I might finally have this figured out, but I need your thoughts. After replacing the pump, I now have a nice 200 bar with no suspension action, and about 100 bar while doing rodeo or pitch at idle. This seems reasonable.

However, I still get a pressure fault and a white warning light. I think this is because the system takes quite a while to build pressure from 0 bar to 200 bar. I read about the "bounce test" and noticed the rear of the car is really bouncy and sitting low, while the front of the car is nice and stiff and sitting higher.

I also noticed that the fluid level in the reservoir seemed really high before I removed the pump, as in, the fluid level was so high it was leaking out the top of the tank.

Does this sound like a failed rear accumulator? This car is driving me crazy, but there are only so many parts left in the system. Let me know what you guys think.

Welwynnick

When you do the bounce test, is that with the engine running, or off?

If the engine is off, you're only bouncing the steel springs - the strut pistons (should) be shut off completely by the isolator valves at each valve block.

Yes, an oil reservoir overflow is typically an indication of a failed accumulator.

Nick

ibeforreal

I had a similar problem where the fluid was overflowing out of the reservoir and I would occasionally get a quick red flashing light on the dash when I went over a bump or railroad tracks. Replaced the accumulator.

One easy way to check the accumulator is to push down on any corner of the car after it has been turned off for about 15 minutes. The car should be very stiff. If one corner seems to dip more so than any other then that is probably where your defective accumulator is. The one on the driver's front side is usually the first to go.

Turboaction

It's easy enough to check the accumulators, so I'll check the front when I'm replacing the rear. The front suspension is stiff when running and shortly after turning the car off, but the rear is more or less always pretty soft. I'm guessing the accumulator basically turns into a big air pocket that never bleeds out once it fails.

ibeforreal

They are basically nitrogen gas chambers that look like a cannon ball. Sometimes they rupture causing the car to become bouncy. See the highlighted areas in the attached picture.

_Ryan

There is an accumulator test in DAS.

Pushing down on the car after it's off will tell you nothing about the accumulators. The shutoff control valve is between the strut and accumulator, isolating the struts from the rest of the system when off.

Turboaction

Ok, so I'm still completely baffled. The accumulators look like they're ok (I removed them and checked to see they weren't ruptured/leaking and still had some pressure (diaphragm fully expanded).

When I start the car after it has been sitting, the car throws a "pressure supply malfunction" code. I believe this is because it takes the car 30 seconds or so to hit the full 200 bar system pressure. From zero, the car his 50 bar almost immediately after startup, then it slowly rises to 200 bar and is stable there.

The car runs the rodeo actuation and is typically over 120 bar, but will dip to about 95 bar minimum during the test.

I've raised and lowered the car 20 times to bleed the air out of the system. I've also bled some fluid out of each of the 4 bleed screws.

If I raise the car from the calibrated height with the ride height button on the dash, the car raises correctly, but when I bring the car back down to the normal ride height two opposite corners stay about 20 mm too high and the other corners stay about 6 mm too high. The car will reach the calibrated height if you run that test.

Any idea where to look next? I'm going to continue running various tests to see if I can figure it out. One question, when performing the load calibration, should the wheels be off the ground? I ran this calibration with the car empty, but all 4 wheels on the drive-on lift.

I'll try to post some more information this weekend when I have some more time to mess with the car.

Turboaction

Ok, I have an update now that I've messed with the car a bit more.

While performing the dynamic test (at 3,000 rpm) the pressure stays above 150 bar. While performing the Rodeo test (at idle) the pressure stays above about 95 bar.

While performing the radial piston pump test, the pressure drop (at 3,000 rpm) is 2. To complete a successful test, the pressure drop should be >2, but then again, it also says for the engine speed to be >3,000 rpm for 5 second. I can't run the engine faster than 3,000 rpm, so I'm not really sure if I'm failing the test or not.

I still trigger a "problem with pressure supply" fault if I turn off the car long enough to bleed down the ABC pressure. This triggers the white ABC light on instrument cluster. If it helps any, the ABC pump seems to make a slightly different sound for the first 15 seconds or so after the car is started, then it becomes more or less silent. Could this be a symptom for why the pump is slow to build pressure?

Let me know if anything seems awry. I did change the pressure regulator block under the car right before I changed the pump, so I may swap that back to my original part to see if the behavior changes. I may also swap the suction valve from my original pump to the reman pump (since I have a low flow symptom). Otherwise, it seems I may need to get another replacement pump (under warranty). Both suction valves pass the electrical test and the suction valve from my old pump seems to actuate just fine (I removed it from the pump and cycled it a few times).

Any help is greatly appreciated.

Turboaction

Ok, I've reached the end of the road. It looks like my reman pump is weak, unless somehow there's some restriction between the tank and the pump.

I changed the regulator valve assembly and the only thing that changed is now the regulated pressure is 195 bar instead of 200 bar. I'm sure it's still within tolerance.

The rodeo test pauses when the pressure drops below 100 bar. I'm sure this isn't normal and is a sign of low pump flow.

I'm unfamiliar with how the suction restrictor valve test works. Whether I apply current to the valve or not, the pressure is the same (the regulated pressure). Since I've never had the diagnostics on a working ABC system, I'm not sure what's normal.

Let me know what you guys think. I don't think there's any way I installed the filter in a way that prevents flow from the tank to the pump. I also don't see how the pump could be partially primed causing this situation considering all of the tests I've ran. If you guys think I should pressurize the fluid tank, let me know. Otherwise, I'll be working on getting another replacement pump.

Welwynnick

Not ignoring you TA, I'm just stuck for any constructive suggestions. It sounds like you're doing the right things. Can you return the pump?

Did you prime the pump? I seem to recall you slackened the belt and spun the pulley. Maybe you could loosen the ABC pipe union at the front corner of the engine sump, so it leaks slightly. Then spin the pump again and make sure only oil comes out? I did something similar with mine, but was on an aftermarket vibration damper U-hose with a screwed termination that allowed for easy bleeding.

I'm not convinced that 100 bar in the rodeo is necessarily a fault anyway. The pump is running at full volume, not full pressure, so it's NOT the normal condition.

I would much rather try to pressurize the ABC tank than have to remove the pump.

Nick

Turboaction

I thought I'd give you guys an update since I've been driving the car the last couple days just to see if anything changes. I'll be calling the parts vendor to get a replacement pump, as it has a very substantial warranty. It makes pressure, just can't quite build the pressure fast enough. There's likely a clearance issue in the cylinders of the pump.

So, once I replace the pump again, I have a new issue to sort out (that was present before the pump issue). When driving, sometimes the left rear strut will quickly drop an inch or more, then pump back up and the car will be perfectly fine. This happened twice before the pump went out, and has happened a few times since I've replaced the pump. There are no codes, so I'm guessing it's either the sensor in the strut, the external sensor, or a wiring connector that's causing a high ride height signal to briefly get to the computer.

I'm not sure which sensor is likely the culprit, but it's probably whichever one is used to determine the ride height (likely the external sensor). I'll read through the documentation a bit more and see if there is a documented troubleshooting procedure for this symptom.

Anyway, I'll post back once I make some more progress. This car really is a pleasure to drive when things are working.

tusabes

I've had that quick drop and correction happen too, very rarely
I haven't looked into what it might be