General Motors Evaporative Control System: Description

An Evaporative Control System (ECS) 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 adsorb 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.