Evaporative Emissions System: Operation

The fuel vapor (check) valve, located on top of the fuel tank, controls the flow of fuel vapors from the tank to the charcoal canister for storage. During normal vehicle operation, fuel vapors are drawn from the charcoal canister into the engine through a hose connected to the air cleaner.

A float valve designed into the fuel vapor valve, prevents liquid fuel from entering the vapor delivery line during severe vehicle operation. The sealed fuel filler cap contains a vacuum and a pressure relief valve.

The vacuum valve relieves tank vacuum caused by a high rate of fuel consumption or cooling of the fuel or fuel vapors. The pressure relief valve in the filler cap prevents excessive fuel tank pressure during heavy engine load or high ambient temperature.