Vehicle is an '04 Cl500, 111K Miles. Having an occasional Red ABC warning, and trying to diagnose. Don't want to just go around adding parts. Warning only comes on after second or later start of the day. Like going to the store, come out and get red warning on start up. Most times I can shut engine off, then restart and red warning goes away. Only see the warning maybe 2 times a month.

When I check on Star system, it shows failure of "Pressure Sensor". However, pressures show 192 bar, and rodeo goes fine. (Bar drops to 110-130 during rodeo) Did Pressure Test on Sensor and get 190+ bar for more than 5 minutes. Fluid level is correct (Bottom of full Engine Off indication when cold, bottom of full Engine On indication when hot ). This tells me the accumulators are probably OK , since the fluid transfers both ways. There is no increase in RPM's when raising or lowering the car, so another sign that the accumulators are ok? No messages on bumps, no hard ride, etc. Tested the Suction Valve via Star, and pressure increased upon actuation a couple of bar, as spec'd. No real issues with the ride, except for the random Red warning. No strut droop when sitting, no visible leaks. Battery and Alternator was checked yesterday and passed tests ( just in case it was a low battery giving strange results).

Only thing I have noticed is bubbles in the fluid when the engine in running. I did replace the Right Rear strut line a few weeks ago ( some seepage at one of the crimps, so replaced as a caution). Did several rodeo's at that time. First two were good, third one Bar dropped to 65 ( maybe oil got hot??). Did another one the next day and Bar was up to 192, and while running the rodeo was at 110-130. Probably driven 100 miles since replacement. The other thing I have noticed the last couple of days is some overflow at the top of the reservoir. This seems strange, since the levels both running and shut down seem normal. Something getting hot, plugged??

I'm hoping that the bubbles, the overflow, and the loss of pressure occasionally ( according to the Red messages) can help you experts help with a diagnosis.

What are your thoughts??

I'm starting to lean toward a pump just starting to go bad, but hate to replace that just because, especially when it gives 192 Bar so easily most of the time.
The pressure sensor could be going bad as well. No leaks in that area, so I think the o-ring is still holding . May replace the o-ring it anyway, just to try. Cheap fix. Sensor is harder to find...
One other thought is the ABC filter might be clogged up. I've only owned the car a few months, going though some of the items that needed fixing. Have not done a fluid "cleanse" or flush, since I wanted to wait until I replaced any bad parts, but have the oil and filter on hand. The ABC Oil in the vehicle was "supposedly " changed within the last couple of years, but who knows. Not filthy black, but not pure green either.

What are your thoughts?? As always, appreciate the help!!

 

Well, I think you've answered some of your own questions; my guess is that there is still some air in the system, which just has to come-out.
Did you use the bleed screws to remove air from the system?

Also, the ABC filter is at the return end of the system, so you won't lose pressure when the filter is clogged.
The only risk of a clogged filter might be that the fluid is not returning to the system quick enough.

That said, I've got about the same. Sometimes when I start the car for a second time after 1 to 4 hours I do get a warning, sometimes white sometimes red. It also lists it as a pressure to low error

I do smell some hydraulic fluid when I'm outside of the car after a drive.

Do you have hydraulic oil on hand?

 

Yes, 5 liters of Pentosin 11 on hand, as well as a new 3 micron filter. I did not use the bleed screws to eliminate the air in the system, since I only did one rear line. Could not find any instructions to do so, and would still have had air in the line from the shock to the bleed nipple, so figured that the rodeo must be the preferred method.

 

Update: Still having same general issues. Red Light coming on after a short drive and stop, like dropping off a package at UPS. Turn off and restart usually clears the red light. I did check the Pressure sensor O-ring. None there, but no leaks. I removed and installed an O-ring just for grins- still no leaks and no change in the problem.

At this point only thing I can figure as the problem is the pump starting to go bad. I hate to change such an expensive item "Just in case", and would like to hear you opinions before I go off and do something stupid!

Thanks!

 

Is the pump leaking around the pulley?
I just came across an interesting thread stating that the hex bolts at the side of the pump come lose.

https://www.benzworld.org/threads/ab...#post-18371194

 

No leak that I can identify. Fluid levels do not drop over time either, another indication of no leaks. If I pull the pump, I will certainly check these out before I replace ( if I can return the new pump??)