DTC P0446: EVAP Vent Control Circuit: Description
WARNING: This page does not describe the selected car, but rather 13 other vehicles, including the 2003 Hummer H2, 2003 GMC Yukon XL, 2003 GMC Yukon, 2003 GMC Sierra, and 2003 GMC Cab & Chassis Sierra. However, it is still accessible from the selected car via links, so may be relevant.
This DTC tests the Evaporative Emission (EVAP) system for a restricted or blocked EVAP vent path. The control module commands the EVAP canister purge solenoid ON and the EVAP canister vent solenoid ON. This allows vacuum to be applied to the EVAP system. Once a calibrated vacuum level has been reached, the control module commands the EVAP canister purge solenoid OFF and the EVAP canister vent solenoid OFF. The control module monitors the Fuel Tank Pressure (FTP) sensor for a decrease in vacuum. If the vacuum does not decrease to near zero inches H2O in a calibrated time, this DTC sets.