WARNING: This page is about a different car, the 2018 Toyota Sequoia, 2017 Toyota Sequoia, and 2016 Toyota Sequoia. However, it is still accessible from the selected car via links, so may be relevant.
P0455 (GROSS LEAK):
EVAP pressure when vacuum introduction complete
Higher than reference pressure x 0.2
P0456 (SMALL LEAK):
EVAP pressure when vacuum introduction complete
Between reference pressure and reference pressure x 0.2