DTC P0446: EVAP Vent Valve Performance: Description
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2002 GMC Savana Special, 2002 GMC Savana Camper Special, 2002 GMC Savana, 2002 Chevrolet RV Cutaway, and 2002 Chevrolet Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
A restricted or blocked Evaporative (EVAP) emission vent path is detected by the control module monitoring the Fuel Tank Pressure (FTP) during normal operation. The control module commands the Evaporative (EVAP) emission vent valve OFF (open), and the EVAP canister purge valve ON (open). The fuel tank pressure should remain low as vacuum is drawn on the EVAP system. If the vent path is blocked or restricted, the vacuum level will increase and DTC P0446 will set.