Evaporative Emissions System: Description and Operation

Evaporative Emission (EVAP) Control System

Refer to the System Diagram to see the functional layout of the system.

EVAP Canister
The EVAP canister temporarily stores fuel vapor from the fuel tank until it can be purged back into the engine and burned.

EVAP Canister Purge Valve
When the engine coolant temperature is below 147 °F (64 °C), the PCM turns off the EVAP canister purge valve which cuts vacuum to the EVAP canister.




Fuel Tank Pressure (FTP) Sensor
The FTP sensor converts fuel tank absolute pressure into an electrical input to the PCM during the EVAP leak check.




EVAP Two Way Valve and EVAP Bypass Solenoid Valve
The EVAP two way valve is installed between the fuel tank and the EVAP canister line.

The EVAP two way valve sends fuel vapor to the EVAP canister corresponding to the pressure inside the fuel tank and prevents excessive vacuum in the fuel tank by drawing in fresh air through the EVAP canister.

The EVAP bypass solenoid valve opens to bypass the two way valve when doing the EVAP leak check.




Evaporative Emission (EVAP) Control Diagram
The 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 drawing fresh air through it and into a port on the throttle body. The purging vacuum is controlled by the EVAP canister purge valve, which is open whenever engine coolant temperature is above 147 °F (64 °C).
- When vapor pressure in the fuel tank is higher than the set valve of the EVAP two way valve, the valve opens and regulates the flow of fuel vapor to the EVAP canister.
- During refueling, the fuel tank vapor control valve opens with the pressure in the fuel tank, and feeds the vapor to the EVAP canister.