How is evaporative emissions testing performed?

Evaporative emissions testing measures fuel vapor losses. Tests include: SHED (Sealed Housing for Evaporative Determination) - vehicle is sealed in chamber while temperature is cycled and hydrocarbon concentration is measured; running loss test - emissions during driving simulation; hot soak - emissions after driving with engine off; refueling test - vapor recovery during fueling. California LEV and EPA regulations have specific test procedures and limits. EVAP system components (canister, valves, seals) must contain fuel vapors and purge them through the engine when conditions allow.