Evaporative Emissions

Evaporative Emissions

The Evaporative Emission (EVAP) system consists of the:

- EVAP (Evaporative Emission) canister purge valve.

- EVAP (Evaporative Emission) canister.

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

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

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 vapor tube.

The fuel vapors are routed:

- from the fuel tank through the vapor vent valve (internal to the tank).

- 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 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 (Evaporative Emission) system.

The EVAP (Evaporative Emission) canister:

- is located on the underside of the vehicle directly below the driver seat.

- contains activated carbon.

- stores fuel vapors.

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 mounted to the EVAP (Evaporative Emission) canister bracket.

The EVAP (Evaporative Emission) canister purge valve:

- is normally closed.

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

- is controlled by the PCM.

- is repaired as a separate item.

- is mounted to the intake manifold.

The EVAP (Evaporative Emission) dust separator:

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

- prevents suspended dust and dirt particles from entering the evaporative emission system.

- is repaired as an assembly with the EVAP (Evaporative Emission) canister vent solenoid.

The EVAP (Evaporative Emission) system monitor:

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

For additional information on the operation of the EVAP (Evaporative Emission) system monitor, refer to Computers and Control Systems Information.

Vehicle Emission Vacuum Routing