LYP

History: 2004 S55 AMG, 72,000 miles ABC warning light came on and scheduled appointment with MB tech. Car sat for about two weeks before going in for diagnostics. Note, ABC warning was no longer displayed and ABC worked normally. MB tech ran diagnostics and claimed I needed a new pump. Tech observed oil leaking from the front seal of the pump while running. I elected to take the car home and consider my options.

Current Status: Sourced a new pump and 20 liters of Pentosin CHF11S. MB tech changed out pump and is now having a difficult time purging the system. Prior to the pump exchange (pretest) the car would rodeo but will not now. New pump reads 192 bar and has good flow back to the ABC reservoir. MB tech claims all voltages and signals good. In frustration MB tech has changed out the accumulator and the control unit with known working assemblies. The car is sitting on its haunches right now but didn't have any leak-down on the solenoids prior to service. Lowered stance is only due to purging exercises. The tech can't get the control valves to raise activate the struts. Two separate valve bodies acting the same way? Tech wants to re-install the original pump but I expressed reluctance due to the significant amount of time this will add to the repair. Flat rate, I probably shouldn't care but my gut says something else is going on here and baffling the MB family of techs. The car has been in the shop for over a week now. Has anyone seen this before? I suggested yanking the front valve body and bench testing it but it's likely going to prove to be OK. My experience with similar issues usually yields something embarrassing but I'm still keen to learn from it.

DRTYLNDY

This is really stumping huh. It almost sounds like the system is flowing just fine but not holding pressure some how. I wonder if the solenoid on the pump is what holds the pressure? I would try and contact Oxygen on here and see if he has an idea.
Good Luck
Johan

LYP

After a review of the manual, I believe the system is locked in passive mode. The shut-off valves are preventing the system from operating even though the ABC controller sees that all is well. An external input is likely causing the valves to lock up. Could be a missing wake-up from a SAM, an error code that hasn't been purged or maybe the ABC believes it is in a reduced load condition that will also lock the shut-offs. Ultimately, I will post the findings. LYP

WHTEVO

Did the tech plug the electrical connector back on the ABC pump after install? Good luck.

Aaron

LYP

Time for an update. The car has been in the shop now approaching 3 weeks. They claim the new pump that I sourced is also faulty. Thank you Aaron, the flow valve on the pump was reinstalled. Dealership has 18 hours invested + new pump and filter. They are now at a point where they don't want to move forward without approval of a small mortgage. Supplier of the pump has a help resource line to help but I'm caught outside the loop right now. I'm sure Schaeffler (LUK) pumps will do everything in their power to help resolve the pump if it is an issue but service will still charge an additional 6+ hrs to re&re the second pump. I don't believe any of us on my end have a good understanding of the radial piston pump function. How does the flow valve work? Is it responsible for opening based on a pressure drop on the pressure sensing transducer?. If the system thinks it is seeing 200 bar then the pump is unlikely to output flow. Can anybody validate my thought process on this. LYP

Viet_Amg408

The reason why tech cannot bleed because the pump is sucking in air mix with abc fluid...cause bubble and over pressure..system shut down.. 200bar is on high side, average 150-160bar.. sound like you have high pressure due to air in system...the new pump is probably bad !

LYP

Dealer believes much the same and a has gone to a lot of trouble to bleed the system. Normal ABC pressure specs for this model should be between 180 - 200 bar. The actual pressure reading on both the old pump and new pump showed 192 bar. No secondary pressure conformation was performed during either test. One anomaly turned up in an email sent by the service rep and that was the pump appeared to build pressure too quickly. I suggest that this could be indicative of a sensor failure though the pump seems to be the main focus. /LYP

LYP

Update 11/22/12, S55 has been in the shop for 4 weeks now. Dealer believed the issue to be a faulty second pump. Sourced a third pump and installed with no change. New pump at 188 bar. So down about 60 psi from last pump. Next focus is on the control valve bodies. Maybe both valve bodies swallowed something at the same time. Keep guessing, we haven't hit on the solution yet. -- LYP

2003_sl55

I am having same problem, would like to hear of a solution. FCAR Scanner gives an error code of C152 502 UNDEFINED.

How does one bleed this system?

WHTEVO

I sure hope you are not paying for three pump changes.

So the pressure's show they are within spec of what you listed above so the pump is obviously working right. Have you guys tried to open the bleeder valves at each corner of the car (same type as what it used to bleed the brake calipers) to maybe check to see if there is actual pressure buildup on the other side of the lines or pump?

Good luck.

Aaron

LYP

I believe I'm on for the first pump. The seal was leaking so its days were numbered but it still doesn't excuse the repair shop going after the red herring issue. Yesterday the valve body was changed out and still nothing. Car has been in shop now for 5 weeks. Collectively we are thinking the pressure feeder line either between the pump and pressure control valve body or the line from the pressure control valve body to the 't' fitting feeding the front and rear control valves could have a blockage. Makes sense because we are seeing pressure and no flow. You would think this is one of the first things that was ruled out before swapping out a pump. ($1700 + 6 hours labor just for a pump) Daimler needs to do something about their prices.

LYP

Thought I was going to get the car back today. Dropped into the shop and saw the car in rodeo mode. I was thrilled and bet everyone wants to know what was going on. Early in the troubleshooting phase a new accumulator was installed to the pressure control valve block without any improvement. The old accumulator was then reinstalled. Apparently a shipping plug was in the new accumulator and ended up in the pressure control valve block (kind of like spitting your gum into your girlfriends mouth) This effectively stopped flow to the main valve blocks of the system. I suspect the reason the car has not been returned yet is because the original issue that the car went in for has now been flagged. Certainly, some lessons have been learned. - LYP

WHTEVO

Hope those lessons weren't on your dime :O Sounds like it's figured out though so that's good.

Aaron

LYP

I agreed to the original pump change and labor. Small change considering the investment by the dealer. I have about 30% invested.(you can do the math if you figure out the cost of pump, oil and labor) Problem is that the stray plug may have introduced particles into the valves causing them to allow the struts to leak down. When the car went in, the shut-offs were OK and the car sat level, afterwards the rear sagged and the RH rear dropped to the ground. Latest news from the dealership is that the rear valve is "bad".
My interpretation is that it sounds like system contamination. 33 years ago, I was a mechanic apprentice and one of my instructors made a comment about the replacement of accumulators. "Be sure to remove the internal dust plug". Ever wonder why?
I'm hoping this string will help future technicians understand the consequences of this kind of error. I'm now an electrical engineer and have often compared electrical with hydraulics because that is where I came from. However, I'm at a loss to compare this kind of failure. Maybe a Lightning strike is the best analogy.