Evaporative Emissions System: Description and Operation: Description and Operation

Evaporative Emissions:

The Evaporative Emission (EVAP) system:
^ is equipped with an On-Board Refueling Vapor Recovery (ORVR) System.
^ prevents hydrocarbon emissions from reaching the atmosphere.
^ stores fuel vapors in the Evaporative Emission (EVAP) canister that are generated during vehicle operation or hot soak, or vehicle refueling, until they can be consumed by the engine.
^ routes the stored fuel vapors to the engine during engine operation.
^ is controlled by the Powertrain Control Module (PCM) which uses various sensor inputs to calculate the desired amount of purge flow. The PCM regulates the purge flow, induced by the application of intake manifold vacuum, by varying the duty cycle applied to the EVAP canister purge valve.
^ has an evaporative emission test port for test purposes.

The fuel vapors are routed:
^ from the fuel tank through the fill limiting vent valve and fuel vapor vent valves.
^ to the EVAP canister through a vapor line.
^ to the engine when the EVAP canister purge valve is opened by the PCM.

The fuel tank pressure (FTP) sensor:
^ monitors the pressure levels in the fuel tank.
^ communicates the pressure reading to the PCM during the OBD II leak test.
^ is located in the fuel vapor valve tube and is serviced as part of the fuel vapor valve tube assembly.

The evaporative emissions canister:
^ is located under the rear of the vehicle near the fuel tank.
^ contains activated carbon.
^ stores fuel vapor.

The fuel tank filler cap:
^ relieves system pressure above 14 kPa (56.21 inches H2O).
^ relieves system vacuum below 3.8 kPa (15.26 inches H2O).

The canister vent solenoid:
^ is normally open.
^ seals the EVAP system for the Inspection And Maintenance (I/M 240) test and OBD II leak and pressure tests.
^ is mounted to the evaporative emission canister.
^ is repaired as a separate item.

The evaporative emission (EVAP) canister purge valve:
^ is normally closed.
^ regulates the purging of the EVAP canister.
^ is controlled by the PCM.

The fuel pump and tank assembly
^ consists of the fill limiting vent valve and fuel vapor vent valve.
^ prevents suspended liquid fuel from being drawn into the evaporative emission canister along with the fuel vapors.

The evaporative emission (EVAP) system monitor:
^ is a self-test strategy within the PCM, which tests the integrity of the EVAP system.
^ monitors the EVAP system for leaks.
^ monitors electronic EVAP components for irrationally high or low voltages.
^ monitors for correct EVAP system operation.
^ uses negative and positive leak test methods to test and activate the EVAP system.

The evaporative emission (EVAP) test port:
^ is used to connect the Evaporative Emissions System Leak Tester to the EVAP system.
^ is located on the EVAP canister purge outlet tube near the EVAP canister purge valve.

The EVAP running loss system leak test:
^ utilizes intake manifold vacuum to test the EVAP system and involves several stages.

The evaporative emission (EVAP) dust separator:
^ is attached to the EVAP canister bracket.
^ prevents suspended dust and dirt particles from entering the EVAP system.
^ is repaired as a separate item.