P0446…Evaporative Emission Control System Vent Control Circuit
Basically, there is a problem in the Evaporative Control System that minimizes the about of gasoline vapor that escapes from your gasoline tank. Unfortunately, it seems to be a common problem on Camrys. My guess is that there may not be a lot of margin between working right and not working right.
What I’d suggest is spending an evening with your favorite search engine researching what causes the code and how to fix it. Be sure and check this link http://www.automotiveforums.com/t248149.html which sounds pretty plausible.
Can you fix it yourself? Strictly speaking, you can fix virtually any automobile problem yourself with enough time, patience, equipment, research, and perseverance. I suspect that if the problem is the cannister control valve, you can probably fix it yourself if you aren’t a total klutz. Fixing the tank bypass valve might be a bit more challenging but still probably possible. If it is something else, you might need to go to a (different) mechanic. FWIW, I have found our 1999 Camry to be a bear to work on because of parts are generally not positioned with replacement in mind.
Can you just ignore the problem? You can of course. And you very well might get away with it. But if you decide to do that, you might wish to buy a code scanner and check every day or so for codes other than P0446.