Evaporative Emissions

The evaporative emission (EVAP) system:

• prevents hydrocarbon emissions from reaching the atmosphere.
• stores the fuel vapors generated during vehicle operation or hot soak in the EVAP canisters 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 powertrain control module (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.
• has an EVAP test port for test purposes.

The fuel vapors are routed:

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

The fuel tank pressure (FTP) sensor:

• is part of the fuel vapor control tube assembly valve.
• monitors the pressure levels in the fuel tank.
• communicates the pressure reading to the PCM during the OBD II leak test.

The fuel vapor control tube assembly valve:

• is located on the top of the fuel tank.
• is used to control the flow of fuel vapors entering the EVAP system.

The fuel vapor control valve:

• prevents the flow of liquid fuel into the EVAP canister or up to the canister purge valve during refueling.
• prevents the collection of liquid fuel in the fuel vapor hoses by overfilling the fuel tank.

The EVAP canisters:

• are located under the vehicle along the left rocker panel.
• contain activated carbon.
• store fuel vapors.

The fuel tank filler cap:

• relieves system vacuum below -3.5 kPa (-14 in H₂ O).

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 left front corner of the EVAP canister bracket.

The evaporative emission EVAP canister purge valve:

• is normally closed.
• regulates the purging of the EVAP canisters.
• is controlled by the PCM.
• is repaired as a separate item.
• is mounted on the cowl.

The EVAP system test port:

• is part of the EVAP canister purge valve.
• is used to connect the EVAP System Leak Tester to the EVAP system.

The evaporative emission EVAP dust separator:

• is attached to the left rear of the EVAP canister bracket.
• prevents suspended dust and dirt particles from entering the evaporative emission system.
• is repaired as a separate item.

The EVAP system monitor:

• is a self-test strategy within the powertrain control module (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 fuel vapor shutoff valve:

• controls fuel tank pressure.
• isolates the fuel tank from the vapor canister.

The EVAP running loss system leak test:

• utilizes intake manifold vacuum to test the system and involves several stages.