2004 MCS, 115K. Several months ago my steering system would lose its power assist under situations of turns to the limit, i.e., certain parking lot maneuvers or u-turns on a narrow street. The power assist would eventually return. I discovered that my fluid level was low and I topped it up with Pentosin CHF11S, the recommended fluid. For a while I thought that solved the problem, but it has now re-occurred, although as before the power assist does return. What explains this? TIA.

 

Sounds like the pump is starting to die a natrual death...
It is just a big dc motor...with brushes..
The brushes wear....and when a worn dc motor encounters a high load situation, it may stop running...the bushes are a common culprut as is the dust from them...but sometimes the windings in the motor can short as they heat up is the insulation is failing...
I would call the unnatrual death the more common constant run on or no run....
Yours seems to br just associated with wear/age as opposed to a different failure mode...

 

How is the fluid level now that the issue has recurred? Could be as simple as a leak.

 

Level is still appropriate.

 

Crap, I knew it wouldn't be that easy. Go with Zippy's answer. The DC motors on these pumps are known to fail, and I've heard of intermittent failures before they finally bite the dust for good. Some people have reported being able to open up the motor, clean out the dust, and install new brushes, as needed. But no matter what repair approach you take, start looking at your options, because it will probably be a matter of time before it's done for good. While I've personally never had issue with mine, I'm thinking about giving my motor a cleaning when I have my subframe down to replace my LCA bushings.

 

Thanks.

 

Drop the PS fan, and drop the PS pump, you will need to drain the fluid from the lines. Open the PS pump up and clean with brake cleaner you will be amazed at the amount of dust (from the brushes that comes out). Watch out for the orange O ring that's under the black cap with the "hose clamp" on it, its fragile. no need to drop the sub frame but if you are then its much easier. Easy to get the PS pump out but a PIA to get back in.

 

I took mine (03) apart about 5 months ago and cleaned it out and put it back in with very little problems. So far I have about 10,000 miles on it since then. My cost was less than $25.

 

Glad to hear another successful motor cleaning. Reinforces my notion that a preventative maintenance cleaning on my 129,000 mile EPS motor be a good idea.