DTC P0456: EVAP System Leak - Very Small Leak: Description
WARNING: This page is about a different car, the 2003 Suzuki XL-7. However, it is still accessible from the selected car via links, so may be relevant.
While running under specific conditions, ECM closes EVAP canister vent valve and opens EVAP canister purge valve. If EVAP control system is okay, EVAP control system pressure detected by fuel pressure sensor is lowered. When EVAP control system pressure is lowered, ECM closes EVAP canister purge valve, leaving EVAP canister vent valve closed. If EVAP system is okay, fuel tank pressure will increase to a predetermined level.