System Description: EVAP: Operation
When fuel tank pressure increases because of heat and fuel vapor generation, evaporated fuel vapors are sent to the EVAP canister where they are stored. When the engine coolant is hot enough, the PCM opens the EVAP canister purge valve to draw the stored fuel vapor in the EVAP canister into the intake manifold to be burned. To regulate the amount of fuel vapor drawn into the engine, the PCM varies the EVAP canister purge valve opening using duty cycle control. When the outside air or other factor cools the fuel tank inside, the fuel tank pressure decreases. The EVAP canister vent shut valve is normally open and allows outside air to enter the fuel tank through the EVAP canister. If there is a system malfunction or blockage in the vent hose, a pressure valve in the fuel filler cap opens and allows outside air to enter preventing system damage. The PCM uses the FTP sensor and EVAP canister vent shut valve to check for leaks in the system. When the enabling conditions are met, the EVAP canister vent shut valve is closed, the PCM monitors for changes in the FTP sensor.