The evaporative emission control system prevents hydrocarbon (HC) vapors from the fuel tank from escaping into the atmosphere where they could form photochemical smog. Gasoline vapors are collected in the charcoal canister. The PCM controls the Purge Control Solenoid Valve (PCSV) to purge any collected vapors from the canister back to the engine for combustlon. This valve is actuated by the purge control signal from the PCM and controls fuel vapor flow from the canister to the intake manifold.

If fuel tank pressure’s value is less than threshold value during "test of vapor generation", the PCM determines that a fault exists and a DTC is stored.