Fuel Evaporation System: Operation
Fuel vapors in the tank build-up until they exceed the pre-set limit of the pressure relief valve, then are vented to canister for storage. The relief valve also allows air to enter the tank, replacing fuel drawn out during engine operation.
When the engine is warming up, the purge hose is shut off by an energized solenoid valve. After engine coolant temperature exceeds 113°F (45°C), the valve opens since current no longer passes through a thermal switch (also part of air injection system on Federal models).