Most carbon canisters for the EVAP system on modern vehicles are mounted very near the gas tank and not under the hood.
The EPA realized that overfilling the gas tank can damage the EVAP system thereby producing more emissions so they demanded the auto makers devise a method to prevent that from happening. So the auto manufacturers came up with the RO/OF valve. ROLL OVER/OVER FILLING valve. This is a ball in a cage with a weight at the bottom at the end of the fill tube. When filling the gas to the full level in the tank the ball floats up and blocks the fill neck thereby shutting off the gas nozzle. And no matter how much you try you can’t overfill the gas tank because the ball prevents gas from being introduced the nozzle keeps shutting off. In the event of a roll-over accident, the weight under the ball forces the ball against the end of the filler neck thereby preventing gas from running out of the gas tank. The EPA doesn’t want unburned gas in the air, in the water, or on the ground.
Tester