DTC P0456: EVAP System - Very Small Leak Detected: Description
WARNING: This page is about a different car, the 2003 Suzuki Aerio. However, it is still accessible from the selected car via links, so may be relevant.
When engine is running, Engine Control Module (ECM) closes EVAP canister vent valve and opens EVAP canister purge valve. If EVAP system is okay, EVAP control system pressure which was detected by fuel tank pressure sensor decreases. After which ECM closes EVAP canister purge valve leaving EVAP canister vent valve closed. If EVAP control system is okay, fuel tank pressure will then increase a specified rate.