Evaporative Emissions: Notes

The Evaporative Emission (EVAP) system consists of the:

• EVAP  canister purge valve.
• EVAP  canister assembly (includes the EVAP canister vent solenoid).
• fuel vapor tube assembly (includes the Fuel Tank Pressure (FTP) sensor).
• Easy Fuel ™ (capless) fuel tank filler pipe

The EVAP  system:

• utilizes an On-Board 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 EVAP  canister assembly:

• is located under the rear of the vehicle, just behind the fuel tank.
• includes the EVAP  canister vent solenoid.
• contains activated carbon.
• stores fuel vapors.

The EVAP  canister purge valve:

• is normally closed.
• regulates purging of the EVAP  canister.
• is controlled by the PCM.
• is direct mounted on the engine.

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 serviced as part of the EVAP  canister assembly and as a separate component.

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

• relieves system vacuum below -3.5 kPa (-16.00 in H ₂ O).

The FTP  sensor:

• is serviced as 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 fuel vapor tube assembly:

• includes the FTP  sensor.
• prevents suspended liquid fuel from being drawn into the EVAP  canister along with the fuel vapors.
• returns the liquid to the fuel tank.
• routes vapors between the canister vent solenoid and the fuel tank filler pipe assembly.

The EVAP  system monitor:

• is a self-test strategy within the PCM which tests the integrity of the EVAP  system. For additional information on the operation of the system monitor, refer to the Introduction - Gasoline Models service information.