Evaporative Emissions: Overview

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

On North American Specification (NAS) market vehicles there is 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.

The vapor generated in the fuel tank during refueling, flows without restriction into the EVAP canister.

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 to the EVAP canister via the tank venting system.

To prevent the charcoal becoming saturated, the fuel vapor is purged from the canister when the engine is running under certain operating conditions. The Powertrain Control Module (PCM) operates the purge valve at the correct times which allows fuel vapor to be drawn from the canister and burnt in the engine.