EVAP Canister Control

Purpose:
The EVAP canister purge system is used to lower HC (hydrocarbon) emission levels by controlling the flow of fuel vapors into the engine, where they are burned along with the normal combustion process.

Operation:
The PCM controls the EVAP canister purge system by energizing and de-energizing the EVAP canister purge solenoid by supplying a ground for the solenoid. When the solenoid is energized, fuel vapors are drawn, by timed vacuum, into the intake manifold where they are burned in the combustion process.

The fuel system used is of the non-venting type. This means that the fuel vapors that build-up inside the fuel tank are not released into the atmosphere. Instead they are directed through a hose to a charcoal canister located in the engine compartment. These fuel vapors are stored within the charcoal canister until the PCM decides that engine conditions are acceptable for the vapors to be drawn from the charcoal canister into the combustion chambers. The PCM uses a normally closed EVAP canister purge solenoid to control these vapors.

With the EVAP canister purge solenoid not energized, a valve within the solenoid body is closed and fuel vapors remain trapped within the charcoal canister. When the PCM supplies a ground for the solenoid, the solenoid energizes and opens the valve. This allows fuel vapors to be drawn by engine vacuum from the charcoal canister into the intake manifold where it will be burned inside the cylinders along with the normal combustion process.