Originally Posted by BimmerM3inGA

Interesting. I can't even see that nut from underneath. But yeah, it took me a while to figure out what was still holding the pump.

It's not a plastic cover, it's some kind of cooling duct. It just ends between the power steering pump and the subframe. It doesn't seem to aimed at anything in particular. It must just be feeding air into the lower part of the engine compartment.