The chain of events:

-Noticed PSE pump running longer than usual and failed to address it.
-PSE quit working (soft close, locks, trunk)
-Found blown 20A fuse, replaced and blew another one after the pump ran for 5 seconds.
-Pulled pump, opened the housing and found one of the nipples for the pump hose completely melted.

My next course of action is locating a housing, which shouldn’t be terribly difficult since W220’s are plentiful at the local Pick n’ Pull. It probably wouldn’t be a bad idea to inspect the impeller for carnage while I’m at it, maybe replace it.

Lastly, I’m sure I have some leaks to chase down to keep this from happening again.

 

KEY LEARNING… address any and all known faults anywhere in the car immediately and as comprehensively as possible.

Carry on.

maw

 

Indeed!

 

This whole thing has turned into a learning experience if nothing else. The dynamic seat pump was successfully replaced with a used unit, however did not resolve the blown fuse issue. The fuse led me to investigate the central locking pump, which also has a burned out motor and melted manifold.

I ordered a used one, it would run for about 15 seconds and then begin struggling to spin. Keep in mind I'm bench testing these with a DC power supply before installation. Assuming the motor was the issue, I swapped a new one into the assembly, same results.

With the pump's rubber hoses removed there was no issue at all. Checking one hose connected at a time, the culprit was the vacuum side, which in turn leads me back to a manifold issue. For what it's worth to rule out the solenoids, I function tested them with 12 VDC and ohm tested them, all were about 33-34 ohms and audibly clicked when power was applied. The entire coil cluster and circuit boards can be removed from the plastic manifold by carefully popping them upwards one at a time. I even swapped them from my old unit just to see if anything would change.

Upon inspecting the manifold ports underneath the coils, one port was plugged with carbon (see pics). I cleared the carbon with a needle and cleaned the bottom of the solenoid plungers because they had carbon deposits as well. After reassembly, same results with the motor running and then gradually hanging up but never stopping completely. I installed it just to see what it would do and it will eventually blow the fuse. At this point the only things I have not changed are the impeller in the pump and the small valve that I believe controls the pump run time (see piece removed with red o-ring). It's also possibly that thee's still an internal blockage in the manifold. I'm not sure it would be wise to introduce carb cleaner to it to attempt to clear it out since there's o-rings and diaphragms inside.

Rather than continue to fight this I'm going to opt for a new unit. Buying used is a crap shoot, whether tested or not because as you can see, there are several internal pieces that can fail or melt. The first picture is from my original pump, note the melted flow path in top center.



Top port is plugged with carbon

I’d you look closely you can see buildup on the plungers vs the ones I’ve already cleaned.

 

Good intel. Carbon on the ports is a new one. Thanks,

maw

 

Yep, you figure 20+ years of normal wear and the carbon dust from the pump impeller is going to go somewhere.