I have performed an evap test with an evap. Tester which pressuerizes the system and times the pressure reading or leakdown time; system pass.
Performed smoke test in several different ways; system pass (no somke detected leaking from front of engine compartment to tank.
I am not clear on the way this system founctions, the 3rd solenoid on the canister which is called the VSV switching valve and the 2 vacuum diaphram also on the canister leaveing me preplexed.

03 Toyota Sequoia 2W/D, DTC P0456 (very small leak)
I am a Ford and Mitsu. Master tech.

There are only two solenoids. Works pretty much like other EVAP systems. After purging canister, the ECM commands a leak test opening EVAP VSV to intake vacuum while the vent valve (CCV) is closed. Vacuum builds in tank and is measured by vapor pressure sensor. If sensor value changes while the system is in vacuum test, it sets a code.

Most common prob is a sticking VSV. Toyota has a TSB (EG020-03R) on this and has updated the part