Evaporative Emissions System - General Motors Evaporative Control System: Description

An evaporative control system (E.C.S.) is used on all General Motors vehicles to reduce gasoline vapor emissions. Vapors are stored in a canister for burning during combustion rather than being vented to the atmosphere.

The fuel tank and usually the carburetor fuel bowl are vented through a hose into a canister containing activated charcoal. The canister absorbs these vapors when the vehicle is parked, and retains them until purged by air drawn through a filter at the bottom of the canister. Purging of the charcoal takes place when the engine is running.