The Evaporative Emissions Control (EVAP) system is designed to keep from escaping into the atmosphere fuel system vapors rich in unburned hydrocarbons. When it's warm outside, vapor from the fuel tank expands and is carried via various valves into the EVAP canister to temporarily store until the vehicle is run. Only under ideal conditions does the Powertrain Control Module (PCM) open the canister purge valve and entry vapors can be mixed with incoming air into the intake manifold where they're combusted in the combustion chambers. These vapors are stored in the EVAP canister, which is typically maintenance free, and contains activated charcoal. Included among the key components are the canister filter, canister vent shut valve, two way valve, the bypass solenoid valve and the fuel tank pressure sensor, all of which provide information and control specialty over vapor flow. When something is wrong, fuel smells common and, most of the time, engine performance suffers too, so you need to know what it is, so check hoses and connections for damage and leaks. The EVAP canister purge valve and the canister assembly can be accessed to perform repairs when the vehicle is raised, while the fuel tank pressure sensor and vent shut valve provide more involved disconnection and installation of various components. Hoses should be properly labeled and new O rings used when reassembling to maintain system integrity.