Evaporative Emissions System: Description and Operation

The evaporative emission system:
- stores fuel vapor with the engine off.
- controls fuel vapor while the engine is running.

Fuel vapor flows from the fuel tank through two evaporative emission valves to the evaporative emissions canister through a vapor line and to the engine when the evaporative emission canister purge valve is opened by the Powertrain Control Module (PCM).

The evaporative emission canister purge valve:
- regulates purging of the evaporative emissions canister.
- is controlled by the powertrain control module.
- contains the evaporative emission test port.

The evaporative emissions canister stores fuel vapor.

The fuel tank pressure sensor:
- monitors the fuel tank pressure.
- communicates the pressure reading to the powertrain control module.

Pressure readings are accessible with the scan tool.

The evaporative emission valve mounts directly to the top of the fuel tank.

The canister vent solenoid valve:
- seals the evaporative emission system for the OBD II leak check.
- can be closed with the scan tool.

The fuel tank filler cap:
- relieves fuel tank pressure above 14 kPa (2 psi).
- relieves fuel tank vacuum below 3.8 kPa (0.53 psi).

Fuel Vapor Valve
A new style evaporative emission valve is used with a head valve which allows a small vapor flow until a predetermined pressure in the fuel tank is reached 2 kPa (8 inches H2O).