When I turn a turn at 25mph-35mph+ I can nnot tighten the turn as the steering gets too hard to turn as if I lost power-assist... does not happen at lower speeds at all - happens in both directions... ANo leaking hoses and fluid in reservoir aplenty .. any thoughts?
Power Steering loss in turns.. on 2003 BMW 540i
Could be your Hydraulic Power Steering System Pump is getting weak or your Steering Rack Spool valve is malfunctioning, meaning the rack and pinion needs replacing or rebuilding. Best to have a sharp Beemer tech make the final call. Hard to do online. Best of Luck!
BMW's have a system of diminished power assist at higher speeds for better stability that could cause this feel but is actually normal operation. If you believe that the issue is excessive and you are sure you have no leaks and a full reservoir than you should have a shop look at it as it will require further diagnosis. Although very few steering boxes go bad on these vehicles it does happen from time to time. I doubt it is a pump as it operates normal at lower speeds.
Power Steering hoses are leaking, replace power steering fluid and check hoses.