Evaporative Emission (EVAP) Canister Purge Check Valve: Notes
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The EVAP canister purge check valve is used on turbocharged engines to prevent boost pressure from forcing open the EVAP canister purge valve and entering the EVAP system. The valve is open under normal engine vacuum. The valve closes during boost conditions to prevent the fuel tank from being pressurized and hydrocarbons forced out of the EVAP system into the atmosphere through the EVAP canister vent valve. When the engine is off, or at atmospheric pressure, the EVAP canister purge check valve is in an indeterminate state. The EVAP canister purge check valve is an integral part of the purge valve assembly.