Test the vent valve on the bench with a 12v battery, Should hold with power/ground applied.
I saw a video of a person doing just this. Sorry for the dumb question, but the vent valve is a 'dumb' device, correct ? It doesn't measure
anything, just gets a signal from the ECU (??) to open and close ?
Two other comments related to this part and my situation....
1) After it first threw the P0455 code, I tightened the gas cap, cleared the code, but it returned after an 8-9 mile drive (on the way to work). It did this (3) times, including once after I cleaned the filler area and gas cap. All of this was with less than a 1/2 tank of fuel. After I filled up (well, not filled, but 3/4 full), I drove almost 50 miles plus a few short errands. Knock on wood, the code hasn't returned.
2) Would a faulty vent valve not allow fuel to be added sometimes ? In the 2-1/4 years that I've owned this, over ~30k miles, I can count on one hand the # of times it's happened, but while fueling up, the gas nozzle clicks off like it's full but it's nowhere near full. Waiting a minute, removing the fill nozzle, etc doesn't help or solve it. I just have to take what fuel it allowed (always plenty, such as 5-10 gallons or sometimes more).