DTC P0455: Evaporative Emission Control System Leak Detected (Gross Leak); DTC P0456: Evaporative Emission Control System Leak Detected (Very Small Leak) [04/2013 - 08/2015]: Description
WARNING: This page is about a different car, the 2015 Lexus IS 250 and 2014 Lexus IS 250. However, it is still accessible from the selected car via links, so may be relevant.
The description can be found in EVAP (Evaporative Emission) System.
Refer to EVAP System [04/2013 - 08/2015]