Description: The evaporative system, sometimes abbreviated as EVAP, consists of the fuel cap, fuel tank, carbon canister, canister purge valve, interconnecting lines and hoses.
Purpose: Contains fuel vapors (hydrocarbons) instead of releasing them into the atmosphere and stores them in a carbon canister. The collected vapors are then routed to the engine where they can be burned. Since evaporative emissions can be a major contributor of pollution from automobiles, a system check is part of an emissions test under an emissions testing program.
Maintenance Tips/Suggestions: The main service item of the evaporative system is the carbon canister filter, if equipped. Check your owner’s manual for specifics on replacing this filter. Beyond that, regular engine performance checks should be all that’s required to ensure proper operation of the evaporative system. A failure in this system could trigger the SERVICE ENGINE SOON or CHECK ENGINE light. If the light appears, have its cause investigated by a professional technician as soon as possible. In areas with an emissions testing program, the gas cap is tested for its ability to hold pressure. If the cap fails, it will need to be replaced in order to pass the test.