Overview - NAS Vehicles Only

The EVAP control system reduces the level of hydrocarbons released into the atmosphere by fuel vapor venting from the fuel tank. The system comprises an evaporative emissions canister, purge valve, DMTL (Diagnostic Module Tank Leakage) pump, DMTL filter, interconnecting vent pipes and hoses.

The system is checked for leak tightness by a DMTL (Diagnostic Module Tank Leakage) pump (part of the evaporative emissions canister), which pressurizes the system and checks for leakage.

Fuel vapor is generated by the fuel in the tank and the amount of vapor produced increases as the fuel heats up. Fuel vapor can flow freely to the evaporative emissions canister via the tank venting system.

The venting system consists of a FLVV (Fuel Limit Vent Valve) and a rollover valve installed in the fuel tank.

The fuel tank vent system connects into a refueling breather pipe that connects to the evaporative emissions canister.

The vapor from the fuel tank passes into the evaporative emissions canister where it is absorbed and stored by the charcoal. Because there is a limit to the amount of vapor the canister can contain, the fuel vapor is purged from the canister when the engine is running and burned in the engine during the combustion cycle.