Evaporative Emissions

The evaporative emission (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 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 fill limit valve and fuel vapor vent valve. The fuel vapor vent valves are part of the fuel tank assembly and cannot be serviced separately.
• to the EVAP canisters through a vapor line.
• to the engine when the EVAP canister purge valve is opened by the PCM.

  The fuel tank pressure (FTP) sensor:

• monitors the pressure levels in the fuel tank.
• communicates the pressure reading to the PCM during the OBD II leak test.

  The EVAP canisters:

• are located on top of the fuel tank.
• contain activated carbon.
• store fuel vapors.

  The fuel tank filler cap (9030):

• relieves system pressure above 14 kPa (56.21 inches H₂ O).
• relieves system vacuum below 3.8 kPa (15.26 inches H₂ O).