DTC P0449: EVAP Vent Valve Performance: Description
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2003 GMC Yukon XL, 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, 2003 Chevrolet Suburban, and 2003 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
An ignition voltage is supplied to the Evaporative Emission (EVAP) canister vent valve. The control module grounds the EVAP canister vent valve control circuit to close the valve be means of an internal switch called a driver. The scan tool displays the commended state of the EVAP canister vent valve as ON or OFF. The control module monitors the status of the driver. If the control module detects an incorrect voltage for the commanded state of the driver, this DTC sets.