Evaporative Emissions

EVAPORATIVE EMISSIONS

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

The evaporative emission (EVAP) system consists of the:
- EVAP canister purge valve.
- EVAP canister.
- EVAP canister vent solenoid.
- fuel vapor tube assembly (includes a grade vent valve and a fuel tank pressure [FTP] sensor).
- dust separator.
- fuel tank filler cap.

The EVAP system:
- utilizes an onboard refueling vapor recovery (ORVR) system that captures the fuel vapors from the vehicle's fuel tank during refueling.
- 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 to the EVAP canister through the fuel vapor tube assembly
- to the engine when the EVAP canister purge valve is opened by the PCM.

The FTP sensor:
- is part of the fuel vapor tube assembly.
- 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 under the rear of the vehicle, just behind the fuel tank.
- contains activated carbon.
- stores fuel vapors.

The fuel tank filler cap:
- relieves system vacuum below 3.8 kPa (15.26 in H2O).

The EVAP 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 attached to the EVAP canister.
- is repaired as a separate item.

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

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

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 abnormally 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 EVAP Running Loss System leak test:
- utilizes intake manifold vacuum to test the system and involves several stages.