WARNING: This page is about a different car, the 2003 GMC Savana and 2003 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: DTC P0446: EVAP Vent System Blocked Or Restricted (Steps 1-6)
Courtesy of GENERAL MOTORS CORP.
Fig 2: DTC P0446: EVAP Vent System Blocked Or Restricted (Steps 7-14)