EVAP System Description
For locations of each component on the vehicle, refer to the Component Location Index .
The evaporative emission (EVAP) controls minimize the amount of fuel vapor escaping to the atmosphere. Vapor from the fuel tank is temporarily stored in the EVAP canister until it can be purged from the canister into the engine and burned. The EVAP canister is purged by the purging vacuum that is controlled by the EVAP canister purge valve. Mexico models: When vapor pressure in the fuel tank is higher than the set value of the EVAP two way valve, the valve opens and regulates the flow of fuel vapor to the EVAP canister. USA/Canada models: Also attached to the EVAP canister vent shut valve and the fuel tank pressure (FTP) sensor.
Operation
USA/Canada models
When fuel tank pressure increases because of heat and fuel vapor generation, the evaporated fuel vapors are sent to the EVAP canister where they are stored. When the engine coolant reaches a certain temperature, the PCM opens the EVAP canister purge valve to draw the stored fuel vapor in the EVAP canister into the intake air 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 on the fuel fill port 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, and the PCM monitors for changes in the FTP sensor.
Mexico models
The evaporated fuel vapors in the fuel tank increases the inside pressure of fuel tank. The increased pressure causes the positive pressure valve to open when the pressure is over the preset value for the EVAP two way valve. The evaporated fuel vapors which passed the EVAP two way valve are sent to the EVAP canister where they are stored. When the engine coolant is reaches a certain temperature, the PCM opens the EVAP canister purge valve to draw the stored fuel vapor in the EVAP canister into the intake air 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 ambient temperature or other factors cool the inside of the fuel tank, the tank pressure decreases. The decreased pressure is negative and opens the negative pressure valve when the pressure is over the preset value of the EVAP two way valve. Since low pressures may deform the fuel tank, outside air is drawn into the evaporative canister through its intake and is routed into the fuel tank along with evaporative emissions. If there is a system malfunction or blockage in the vent hose, a pressure valve on the fuel fill port opens and allows outside air to enter preventing system damage.