DTC P0496: EVAP System High Purge Flow: Description
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.
This DTC tests for undesired intake manifold vacuum flow to the Evaporative Emission (EVAP) system. The control module seals the EVAP system by commanding the EVAP canister purge valve OFF and the EVAP canister vent valve ON. The control module monitors the Fuel Tank Pressure (FTP) sensor to determine if a vacuum is being drawn on the EVAP system. If vacuum in the EVAP system is more than a predetermined time, this DTC sets.
If the control module command is ON the EVAP purge valve is OPEN and the EVAP canister vent valve is CLOSED. If the control module command is OFF the EVAP purge valve is CLOSED and the EVAP canister vent valve is OPEN.