EVAP System Description

For locations of each component on vehicle, refer to Component Location Index

Overview 

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 drawing fresh air through it and into a port on the intake manifold.

The purging vacuum is controlled by the EVAP canister purge valve(s).

With EVAP two way valve: 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.

Operation 

When fuel tank pressure increases because of heat and fuel vapor generation, evaporated fuel vapor is sent to the evaporative emission (EVAP) canister.

When the engine coolant is hot enough, the powertrain control module (PCM) opens the EVAP canister purge valves 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 valves opening using duty cycle control.

The PCM commands one purge valve open, once the duty cycle is at 100%, the second purge valve will be commanded open to increase the flow of the fuel vapor.

When the outside air or other factor cools the fuel tank inside, the tank pressure decreases.

The canister change over valve in the EVAP leak check module is normally open when not energized, and allows outside air to flow in and out of the EVAP canister.

The PCM uses the EVAP leak check module to check for leaks in the system.

Courtesy of HONDA, U.S.A., INC.

EVAP Leak Check Module 

The EVAP leak check module (ELCM; mounted on a bracket to the side of the EVAP canister) is a small vacuum pump used to check the leakage of the EVAP system to create a vacuum in the system. The EVAP leak check module pressure sensor, the canister change over valve, and the EVAP leak check module vacuum pump are inside the ELCM.

The canister change over valve is normally open when not energized. When open the valve allows air to flow in and out of the EVAP canister. When energized the valve seals the EVAP canister side of the system from the atmosphere.

Courtesy of HONDA, U.S.A., INC.