DTC P0455 Evaporative Emission Control System Leak Detected (Gross Leak); DTC P0456 Evaporative Emission Control System Leak Detected (Very Small Leak): Description
WARNING: This page is about a different car, the 2008 Lexus IS 350. However, it is still accessible from the selected car via links, so may be relevant.
The circuit description can be found in the EVAP (Evaporative Emission) System (See DESCRIPTION ).