Evaporative Emissions System: Description and Operation

Fig. 18 Evaporative Control System:

When the vehicle is stopped and the engine is OFF, or while sitting on an incline, the fuel vapors are collected in the vapor separator where some of them condense and flow back to the fuel tank. The vapor continues to the charcoal canister in the engine compartment where it is absorbed in the activated charcoal until the engine is started.
After starting, vacuum causes airflow over the charcoal which releases the fuel vapors. The vapors are then drawn into the engine and burned.
The vapor separator is also used as an expansion tank, as it is capable of compensating for the expansion of a full fuel tank when temperatures rise above 27°C (80°F).