Hi,
The Posche Diagnostic procedure for P0446 states:
- Possible Causes of Fault:
- Air line plugged
- Tank Vent stuck in the open state (vacuum continuously enters the Tank System from the Intake pipe)
- Activated Charcoal Shutoff Valve is plugged/stuck in a closed state
- Flow resistance of the Activated Charcoal Filter is too high (Filter deformed/plugged)
- Pressure Sensor closes incorrectly (Polarity reversal)
The procedure then goes on to say to replace the Activated Charcoal Cannister, if previously replaced, replace the Shutoff Valve. There is also a procedure to blow compressed air into the Purge Air Line. Most of these components live under the Passenger side Front Wheel Well Liner. Hope this helps...
Happy Motoring!... Jim'99