what does an evap canister do
EVAP Canister Purge Valve. When energized, the evaporative canister purge valve allows the fuel vapor to flow from the EVAP canister to the engine. The normally closed valve is pulse width modulated by the PCM in order to precisely control the vapor flow.VAP Vent Valve. The evaporative canister vent valve not only allows the fresh outside air to the EVAP canister during the purge modes, but also allows the diagnostic to pull a vacuum on the fuel tank by closing the vent valve.