Malfunctioning Power-Steering on 2003 BMW 540i at speeds above 30 mph in turns

I bought this car in 2006 used and love it… but lately it has developed a nasty steering issue (last 6 months) … Whenever I take a turn at speeds above 30 mph, it seems like I lose power steering and it gets real hard to turn the steering wheel. It is fine at lower speeds, and sometimes sharp wiggling suddenly seems to engage it… BUT it is a repeatable failure… Had the system flushed, but before I start ripping out compentns and replacing them, is there anyone out there that can shed some light on this so I am not totally dumbfounded and shelling out $$ without a plan?

What are you doing road course type driving? Its hard for me to tell the P/S is even working at speeds above 30mph.

There is a rather expensive hydraulic control unit that sits on top of the steering box (your car has a box) that could be the cause.

Typical road-course driving is fine, as this problem seems to only happen when the steering-wheel deflections I am making are for say 90degreee or hairpin turns requiring a decent (have not measured the wheel-angle) steering-angle… which I typically do not take at high speeds… in regular highway and back-road driving (gentle turns)I simply can not feel anything wrong as I do not make ‘large’ steering wheel adjustments. I can still turn the wheel so it is not really a safety hazard (yet), it just takes far more effort than I think it should and I am/was used to… I am just ambivalent of where to start troubleshooting (or at least telling my mechanic to do so) so as to not start replacing items willy-nilly… If there was even a suggestion as to what or where to replace/look to make a better plan or repair/replacement, I would be happy… Thx for your interest and willingness to provide advice… (:slight_smile:

You most likely have a bad steering pump. I know a few other 540 guys that have had this same problem. I got a used pump at the local junk yard for ~$150, new is about $450 just for the pump. It’s about an hour job to replace it. Mine was ripped off it’s mounts when the alternator seized.
I have a 2000 540i 6 speed. You can try to take the pump apart and see if there is anything obviously wrong. I didn’t see any internal problems when I opened a defective pump that a friend gave me.

I will put this to my Master Tech friend, you have eliminated belt slippage haven’t you? I was gone from BMW in 2003 and did not see the problem on earlier e-39’s,my favorite BMW to make money on and the M5 was a ultimate thrill to drive.