Evaporative Emissions: Notes

The Evaporative Emission (EVAP) system consists of the:

• EVAP canister.
• EVAP canister purge valve.
• Dual check valve (2.0L Gasoline Turbocharged Direct Injection (GTDI) engine) (part of the canister purge valve)
• Vapor ejector (2.0L GTDI engine) (part of the canister purge valve)
• EVAP canister vent solenoid (includes the dust separator).
• Fuel vapor tube assembly (includes the Fuel Tank Pressure (FTP) sensor).

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 vapor tube.

The fuel vapors are routed:

• from the fuel tank through the vapor vent valve (internal to the tank).
• to the EVAP canisters through a vapor tube.
• from the EVAP canister to the engine when the EVAP canister purge valve is opened by the PCM.

The FTP 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 II leak test.

The fuel vapor tube assembly:

• is a 2-piece assembly.
• is located midway under the vehicle along the LH frame rail.
• is used to route the flow of fuel vapors entering the EVAP system.

The EVAP canister:

• is located on the underside of the vehicle directly below the driver seat.
• contains activated carbon.
• stores fuel vapors.

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 mounted to the EVAP canister bracket.

The EVAP canister purge valve:

• is normally closed.
• regulates the purging of the EVAP canister.
• is controlled by the PCM.
• is repaired as a separate item.
• is mounted to the intake manifold.

The dual check valve (2.0L GTDI engine):

• routes fuel vapors to the intake manifold when the intake manifold is not pressurized.
• routes fuel vapors to the vapor ejector when the intake manifold is pressurized.

The vapor ejector (2.0L GTDI engine)

• is a venturi
• uses pressurized air from the turbocharger-to-Charge Air Cooler (CAC) tube to route fuel vapors to the Air Cleaner (ACL) outlet tube.

The EVAP dust separator:

• is attached to the EVAP canister vent solenoid mounted on the EVAP canister bracket.
• prevents suspended dust and dirt particles from entering the evaporative emission system.
• is repaired as an assembly with the EVAP canister vent solenoid.

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 EVAP system monitor, refer to the INTRODUCTION - GASOLINE MODELS .