DTC P0455, P0456: Evaporative Emission Control System Leak Detected (Gross Leak) (2006/01-); Evaporative Emission Control System Leak Detected (Very Small Leak) (2006/01-): Description
WARNING: This page is about a different car, the 2006 Toyota Land Cruiser. However, it is still accessible from the selected car via links, so may be relevant.
The circuit description can be found in the Evaporative Emission (EVAP) system (see EVAP System (2006/01-) ).