DTC P2420: Evaporative Emission Pressure Switching Valve Stuck OFF [12/2015 - 08/2016]: Description
WARNING: This page is about a different car, the 2016 Toyota Sienna. 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 DESCRIPTION ).