2001 Prizm PO446 code-help?

[buckyball1]

Hi--I am new to the forum and hope asking about a "Prizm" isn't off-topic and outside the forum rules, if so i apologize

here's summary info on problem
1. 2001 Prizm check engine light on since 45,000 miles (car now has 137,000) and i always overfilled the gas tank
2. car runs fine
3 car will need to pass OBCII test for emission control in Portland, OR where my daughter is moving
4. light always goes off for months during the winter, then back on in warmer weather
4. 3 years ago for $400 a mechanic replaced an 'evap sensor' , then an 'evap solenoid' (not sure what the really meant) and he said, 'i may have bent a pin doing it'-no help
5. code curretnly shown is PO446 "EVAP Emission Control Circuit vent valve Malfunction"

I talked to local Toyota dealer (good reputation) and a local garage (also highly recommended by people i trust)--both suggested essentially the same thing--start with a diagnostic with their $$ scanner, then a "smoke test", then evaluate results before deciding whether to try to fix. I understand the system, has 3? valves (one under the hood and two in the rear?) and a charcoal canister. I suppose it could be any of these (or more than one)or a hose or....While i don't like the $ we're talking about, my real fear is spending $250-500 and NOT having it fixed.


and moving on..a little knowledge is a dangerous thing, but i've found diagrams and explanations of how canister system works with the multiple valves and loops- CCV/vent , several VSV/purge and bypass, and if PO446 is correct and only code, it would indicate problem is with the vent/CCV part of the system

we have to fix this for my daughter to register the car
suggestions on how to proceed and which place to take it to?

thanks---jim