Evaporative Emission (EVAP) Check Valve
WARNING: This page is about a different car, the 2003 Mazda Tribute. However, it is still accessible from the selected car via links, so may be relevant.
The check valve vent is normally closed. When the EVAP system enters a purge cycle, the valve forces the purge air, being drawn in, to enter the system through the remote canister vent tube. During refueling the valve vent opens allowing the displaced air to vent freely to the atmosphere through a more direct and lower resistance path.