Just bought a 2004 Grand Prix GTP w/ 160K miles (and has Magnasteer). It came with a pretty loud P/S whine but drove ok. It would also turn on the ABS & T/C lights when turning far left or right. Based on the mileage I decided to go ahead and replace the pump, the rack & pinion and pressure line. Not the return line though as it was not leaking but flushed it out. Filled the system and bled it with the wheels in the air. After running for a few minutes, it still had the whine even though all air had been bled by turning wheels left and right approx. 30 times. No ABS or T/C lights. Put the car on the ground and went to back out and at idle had zero power assist. Could rev up and would get some assist. Figuring I had a dud of a pump, replaced the pump again. On the first drive it was sticky when I would come to a stop but got better and drove for about 25 minutes. When slowing to turn around in a cove, either left or right still have a loud whine and I can feel a little jerkiness in the steering wheel. At highway speeds I can tell the magnasteer is working. Process of elimination says that the return line maybe is allowing air to be sucked in (even though when I stop and look at the reservoir with it running there is NO foaming) or a blockage in the line?? I inspected it for crimps or damage and found none. The only other thing I guess could be the computer control of the magnasteer. Any ideas? (I do not get the ABS & T/C lights anymore with either pump so that must have been in the magnasteer part of the old rack.)
