Toyota: Toyota Celica code PO446, toyota celica gt, charcoal canister

Question
My girlfriend has a 2001 Toyota Celica GT with the check engine light on.  I have used my Mac Tools scanner to grab the codes and info and found history codes PO440 (emmisions system malfunction) and new code PO446 (vent circuit malfunction)  The car has been repaired at the dealership where they installed a new charcoal canister and erased the code and turned off the light.  The light came back on and I scanned it and found that it has not been fixed.  I bought a new vent cap and put it on and erased the codes and turned the light off.  It has now come back on with a new code PO446.  Is it the purge solonoid?  Possibly a bad charcoal canister from Toyota?  Maybe even O2 Sensor(s).  Help is appreciated.  The performance of the car has not been affected in any way either.

Answer
The VSV valve is the next thing to check.  The O2 sensor can also be replaced but being that the car is relatively new, it shouldn't be an issue.  As far as receiving a "faulty" canister from Toyota, highly doubtful as they aren't anything you can make wrong.  It's just activated charcoal that vents your fuel tank.