Evaporative Emissions System: Description and Operation

PURPOSE
The fuel evaporative emission system allows for controlled release of fuel tank pressure through a evaporative emission canister. Under normal operating conditions, this system will allow sufficient venting to prevent a build-up of internal fuel tank pressure.

FUEL TANK EVAPORATIVE EMISSION SYSTEM COMPONENTS
- fuel tank and fuel tank filler pipe.
- pressure/vacuum relief fuel tank filler cap.
- evaporative emission valve with open flow to vacuum and pressure relief.
- evaporative emission tube and evaporative emission hoses.
- evaporative emission canister.

ENGINE EVAPORATIVE EMISSION SYSTEM COMPONENTS
- evaporative emission canister purge valve (CANP).
- evaporative emission canister. System control and operation are accomplished through separate basic functions in the system:
- fill control vent system
- fuel tank evaporative emission venting and storage system
- evaporative emission purge system
- fuel tank filler cap and evaporative emission valve

Some operating conditions may cause temporary build-up of internal fuel tank pressure. Some of these conditions are:
- parking the vehicle after filling the fuel tank on warm or hot days. The fuel is cool from underground storage and vaporizes rapidly when warmed.
- parking after driving over rough roads, washboard, or other harsh surfaces, after filling the fuel tank. Agitation of fuel increases vaporization.
- parking after driving long distances in high temperature conditions.
- climbing long grades, especially while towing a trailer or while vehicle is fully loaded.

No service is required if these conditions caused the customer concern. A normally functioning fuel tank evaporative emission system will relieve the pressure build-up.