Evaporative Emissions System: Description and Operation

EVAP Canister:

EVAP System:

The Evaporative Emission (EVAP) control system used on all vehicles is the charcoal canister storage method. This method transfers fuel vapor from the fuel tank to an activated carbon (charcoal) storage device (canister) to hold the vapors when the vehicle is not operating. When the engine is running, the fuel vapor is purged from the carbon element by intake air flow and consumed in the normal combustion process.

The Evaporative Emission (EVAP) control system uses a 1500 cc charcoal canister to absorb fuel vapors from the gas tank.

When gasoline vapor builds enough to overcome the spring tension of the EVAP pressure control valve, the vapor will flow to the canister where it is absorbed and stored by the charcoal. Under certain operating conditions the PCM will command the purge solenoid valve to open. This allows the vapor to flow into the intake manifold for combustion.

This system has a remote mounted canister purge control solenoid valve. The PCM operates this solenoid valve to control vacuum to the canister. Under cold engine or idle conditions, the solenoid valve is dosed, which prevents vacuum from being applied to the canister. The PCM activates (or opens) the solenoid valve and allows purge under the following conditions:
^ Engine is warm.
^ After the engine has been running a specified period of time.
^ Above a specified road speed.
^ Above a specified throttle opening.

LEGEND IMAGE (1)
(1) Tank Tube
(2) Air Tube (Fresh Air inlet)
(3) Purge Tube

LEGEND IMAGE (2)
(1) Throttle Body
(2) EVAP Solenoid Valve
(3) EVAP Vacuum Switch
(4) EVAP Canister
(5) EVAP Pressure Control Valve
(6) Floating Roll-Over Valve
(7) Fuel Tank