Evaporative Emissions - Overview (G1772571): Overview

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The Evaporative Emission (EVAP) system reduces the levels of hydrocarbons released into the atmosphere by fuel vapor venting from the fuel tank. The system comprises an Evaporative emissions canister, a purge valve and interconnecting vapor pipes. The vapor pipes are connected to the system components using quick release connectors.

North American Specification (NAS) market vehicle have an additional Diagnostic Module Tank Leakage (DMTL) system. The DMTL system allows the fuel vapor system to be pressurized and detect if a leak is present.

Fuel vapor is generated by the fuel in the fuel tank. The amount of fuel vapor produced increases as the fuel temperature rises. Fuel vapor can flow freely into the evaporative emissions canister via the tank venting system.

On all vehicles, the vapor generated in the fuel tank during refueling, flows without restriction into the Evaporative emissions canister.

Fuel vapor passes into the Evaporative emissions canister where it is absorbed and stored in porous activated charcoal contained within the canister. To prevent the charcoal becoming saturated, the fuel vapor is purged from the canister when the engine is running under certain operating conditions. The Engine Control Module (ECM) operates the purge valve at the correct times which allows fuel vapor to be drawn from the canister and burnt in the engine.