A leaking p/s switch can damage the O2 sensors. Fluid can wick through the harness. Pull the connectors and look for p/s fluid.

2003 uses MS9602 which is ATF+4

Check the belt like '98 says for glazing and the tensioner too.

 

Belt looks good, tensioner is strong. No fluid leaks at all

 

Then it's the pump or the rack. You can test the p/s pump.

 

So it's definitely couldn't be the switch?

 

The switch kicks the RPM up when under heavy load, such as turning at idle, so that the engine doesn't stall. When it leaks it can allow p/s fluid to get into the PCM and O2 sensors.

The switch does not control pump output directly.

 

check fluid level snow/water in the pump. water gets in and pushes the fluid out. Happen to myself with flooded streets.

 

I installed a reman cardone pump, I have power steering again but it has a constant low whine to it. Almost can't hear it, but it's still enough to get on your nerves considering it wasnt making any noises before.

 

A lot of the reman pumps have that problem not sure why but many have complained about that on this forum.

Reman is never as good as new but cost way less

New OEM pump around $300