EVAP System Operation

The Evaporative Emission (EVAP) control system limits the fuel vapors from escaping into the atmosphere. Fuel tank vapors are allowed to move from the fuel tank due to pressure in the tank, through the vapor pipe, into the EVAP canister. Carbon in the canister absorbs and stores the fuel vapors. Excess pressure is vented through the vent line and the EVAP vent solenoid to the atmosphere. The EVAP canister stores the fuel vapors until the engine is able to use the fuel vapors. At an appropriate time, the PCM will command the EVAP purge valve open, allowing the engine vacuum to be applied to the EVAP canister. When the EVAP vent valve is open, fresh air will be drawn through the valve and the vent line to the EVAP canister. Fresh air is drawn through the canister, pulling the fuel vapors from the carbon. The air/fuel vapor mixture continues through the EVAP purge pipe, and through EVAP purge valve into the intake manifold to be consumed during normal combustion. The EVAP system requires the PCM be able to detect a leak as small as 0.049 inch in the EVAP system. The PCM uses several tests in order to determine if the EVAP system is sealed.