Thanks for advice. Still not sure what I can do here, though. From research I did, believed it was the vent valve too, and thought this was the part:

http://www.ebay.com/itm/291533008513?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
Been clearing the code, it keeps coming back. What I find most odd about this is that it kicked in after a massive rainstorm -- no garage, so car is outside under a cover -- and I've always had weird issues with heavy rains doing something to the electrical, triggering false codes, causing the spoiler to rise up on its own, etc. So kind of operating under the partial assumption that this P0446 is BS, although whenever this happened before the code either vanished on its own or I'd clear it with my code reader and it would stay gone.

Anyhow, annoying. That Check Engine light makes it impossible for me to enjoy driving the damn car, kicks in the old OCD even though I'm 99% sure this is pretty much meaningless. I wish you could just hide codes for good. This seems more like a nuisance code than anything else.