Evaporative Emission System

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 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 EVAP test port for test purposes.

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

The EVAP canister:
- is located under the right rear of the vehicle.
- contains activated carbon.
- stores fuel vapor.
- includes a fresh air transfer tube, routing fresh air between the canister vent solenoid hose and the fuel tank filler door pocket.

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

The EVAP canister vent solenoid:
- is normally open.
- seals the EVAP system for the inspection and maintenance (I/M 240) test and OBDII leak and pressure tests.
- is mounted to the EVAP canister.
- is repaired as a separate item.

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

The fuel vapor control tube assembly valve:
- is located under the rear of the vehicle.
- is used to control the flow of fuel vapors entering the EVAP system.
- prevents suspended liquid fuel from being drawn into the EVAP canister along with the fuel vapors.

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

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 and positive leak test methods to test and activate the EVAP system.

The EVAP test port:
- is used to connect the Evaporative Emission System Leak Tester to the EVAP system.
- is connected to the purge valve located in the engine compartment.

The EVAP Running Loss System Leak Test:
- utilizes intake manifold vacuum to test the EVAP system and involves several stages.