Evaporative Emissions System: Description and Operation

Evaporative Emission Control System Schematic:

The evaporative emission control system used on this vehicle is the charcoal canister storage method. This method transfers fuel vapor from the fuel tank to an activated carbon storage canister to retain 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.

Vapor Canister:

VAPOR CANISTER
Gasoline vapors from the fuel tank flow into the tube labeled "Tank". Any liquid fuel goes into a reservoir in the bottom of the canister to protect the carbon bed above. These vapors are absorbed into the carbon. The canister is purged when the engine is running above idle speed. Ambient air is allowed into the canister through the air tube in the top. The air mixes with the vapor and is drawn into the intake manifold.

Canister Purge Solenoid:

EVAPORATIVE CONTROL
The ECM operates a solenoid valve which controls vacuum to the purge passage in the charcoal canister. Under cold or idle conditions, the solenoid is turned "ON" by the ECM which blocks vacuum to the canister purge passage. The ECM turns "OFF" the solenoid valve and allows purge when:

Engine is warm.
After the engine has been running a specified time.
Above a specified road speed.
Above a specified throttle opening.