Evaporative Emissions

EVAPORATIVE EMISSIONS

NOTE: The vehicle vacuum routing diagram are contained in the Description and Operation subsection of the Engine Emission Control. Refer to Emission Control Systems.

The evaporative emission (EVAP) system consists of the:
- dust separator.
- EVAP canister.
- EVAP canister purge valve.
- EVAP canister vent solenoid.
- EVAP filter assembly tube (empty housing).
- fuel vapor tube assembly containing a fuel tank pressure sensor.
- vapor tubes.
- vapor hoses.

The EVAP system:
- prevents hydrocarbon emissions from reaching the atmosphere.
- stores fuel vapors in the EVAP canister that are generated during vehicle operation or hot soak, until they can be consumed by the engine during normal engine operation.
- routes the stored fuel vapors to the engine during engine operation.
- is controlled by the PCM which, using various sensor inputs, calculates 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.

The fuel vapors are routed:
- from the fuel tank through the fill limit valve and fuel vapor vent valve. The fuel vapor vent valves are part of the fuel tank assembly and cannot be serviced separately.
- to the EVAP canisters 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.

The EVAP canister:
- is located on top of the spare tire.
- contains activated carbon.
- stores fuel vapors.

The fuel tank filler cap:
- relieves system vacuum below 3.5 kPa (14.0 inches H2O).

The canister vent solenoid:
- is normally open.
- seals the evaporative emissions system for the inspection and maintenance (I/M 240) test and OBD II leak and pressure tests.

The EVAP canister purge valve:
- is normally closed.
- regulates the purging of the EVAP canister.
- is controlled by the PCM.

The EVAP dust separator:
- prevents suspended dust and dirt particles from entering the EVAP system.
- is serviced as a separate item.

The 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 leak test methods to test and activate the EVAP system.
- a FUEL CAP message will be displayed by the message center if the EVAP system fails the test or after a fill-up the cap is installed incorrectly or leaks.
- a check engine light will illuminate if the EVAP system leaks.

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