Evaporative Emissions

Evaporative Emissions

The Evaporative Emission (EVAP) system consists of the:

- EVAP (Evaporative Emission) canister purge valve.

- EVAP (Evaporative Emission) canister (includes the dust separator and the vent solenoid).

- fuel vapor tube assembly (includes the Fuel Tank Pressure (FTP) sensor and the vapor blocking valve).

- Easy Fuel(TM) (capless) fuel tank filler pipe.

The EVAP (Evaporative Emission) system:

- prevents hydrocarbon emissions from reaching the atmosphere.

- stores fuel vapors in the EVAP (Evaporative Emission) 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 (Evaporative Emission) canister purge valve.

The fuel vapors are routed:

- from the fuel tank through the fuel vapor vent valve.

- to the EVAP (Evaporative Emission) canisters through a vapor tube.

- from the EVAP (Evaporative Emission) canister to the engine when the EVAP (Evaporative Emission) canister purge valve is opened by the PCM.

The FTP (Fuel Tank Pressure) sensor (part of fuel vapor tube assembly):

- monitors the pressure levels in the fuel tank.

- communicates the pressure reading to the PCM during the OBD (On-Board Diagnostic) II leak test.

The fuel vapor tube assembly:

- is located under the rear of the vehicle.

- is used to monitor fuel pressure and relay information to the PCM.

- includes the FTP (Fuel Tank Pressure) sensor and the vapor blocking valve.

The EVAP (Evaporative Emission) canister:

- is located under the rear of the vehicle.

- includes the dust separator and vent solenoid.

- contains activated carbon.

- stores fuel vapors.

The Easy Fuel(TM) (capless) fuel tank filler pipe:

- relieves system vacuum below -3.5 kPa (-16.00 in H2O).

The EVAP (Evaporative Emission) canister vent solenoid:

- is normally open.

- seals the EVAP (Evaporative Emission) system for the inspection and maintenance (I/M 240) test and OBD (On-Board Diagnostic) II leak and pressure tests.

- is serviced as part of the EVAP (Evaporative Emission) canister.

The EVAP (Evaporative Emission) canister purge valve:

- is normally closed.

- regulates the purging of the EVAP (Evaporative Emission) canisters.

- is controlled by the PCM.

- is repaired as a separate item.

- is mounted to the intake manifold.

The dust separator:

- is attached to the EVAP (Evaporative Emission) canister vent solenoid.

- prevents suspended dust and dirt particles from entering the EVAP (Evaporative Emission) system.

- is serviced as part of the EVAP (Evaporative Emission) canister.

The EVAP (Evaporative Emission) system monitor:

- is a self-test strategy within the PCM which tests the integrity of the EVAP (Evaporative Emission) system.

- monitors the EVAP (Evaporative Emission) system for leaks.

- monitors electronic EVAP (Evaporative Emission) components for irrationally high or low voltages.

- monitors for correct EVAP (Evaporative Emission) system operation.

- uses negative and positive leak test methods to test and activate the EVAP (Evaporative Emission) system.

The engine ON EVAP (Evaporative Emission) leak-check monitor:

- is executed by the individual components of the enhanced EVAP (Evaporative Emission) system. Intake manifold vacuum is utilized to reach a target vacuum on the EVAP (Evaporative Emission) system. The FTP (Fuel Tank Pressure) sensor is used by the engine ON EVAP (Evaporative Emission) leak-check monitor to determine if the target vacuum necessary to carry out the leak-check on the EVAP (Evaporative Emission) system has been reached. Once target vacuum on the EVAP (Evaporative Emission) system is achieved, the change in EVAP (Evaporative Emission) system vacuum over a calibrated period of time determines if a leak exists. Testing and Inspection

The Engine Off Natural Vacuum (EONV) EVAP (Evaporative Emission) leak-check monitor is executed:

- once the engine ON EVAP (Evaporative Emission) leak-check monitor is completed and the key is turned OFF. The EONV (Engine Off Natural Vacuum) EVAP (Evaporative Emission) leak-check monitor determines if a leak is present when the naturally occurring change in the fuel tank pressure or vacuum does not exceed a calibrated limit during a calibrated amount of time. A separate, low-power consuming microprocessor in the PCM manages the EONV (Engine Off Natural Vacuum) leak-check. The engine OFF EVAP (Evaporative Emission) leak-check monitor is executed by the individual components of the enhanced EVAP (Evaporative Emission) system.

Vehicle Emission Vacuum Routing