Evaporative Emissions System: Description and Operation

PURPOSE
The evaporative emissions system prevents the escape of hydrocarbon emissions into the atmosphere under HOT SOAK and engine OFF conditions by storing the fuel vapors in the evaporative emissions canister. The system also controls the purging of stored fuel vapors from the evaporative emissions canister to the engine when the vehicle is being operated.

OPERATION
Fuel vapors trapped in the fuel tank are vented through two evaporative emissions valves located on top of the fuel tank. They allow the fuel vapor to pass into a vapor line to the evaporative emissions canister through the evaporative emissions canister purge valve. The fuel vapors are stored in the evaporative emissions canister mounted on the rear crossmember. When the vehicle is being operated, fuel vapors are purged from the evaporative emissions canister into the engine by means of the fuel vapor management valve.

COMPONENTS
A fuel vapor tube runs from the evaporative emissions canister to the fuel vapor management valve located in the upper left corner of the engine compartment. The fuel vapor management valve will open and close to maintain the correct vacuum in the evaporative emissions system. From the fuel vapor management valve through a fuel vapor tube, the fuel vapors travel to the engine, allowing the vapors to be purged from the evaporative emissions canister.

A fuel tank pressure sensor (located in the fuel tank) monitors vacuum levels in the evaporative emissions system. If the vacuum level is too low or drops too rapidly, the fuel tank pressure sensor will signal the powertrain control module to set a Diagnostic Trouble Code (DTC).