Evaporative Emissions System: Description and Operation

Evaporative emissions (EVAP) system

Leak diagnosis, functional description

The Evaporative emissions system (including fuel tank) is equipped with leak diagnosis capability which will detect if the system is leaking.

The diagnostic function operates by pressurizing the system and is capable of sensing leakage in cases where the source is at least 1 mm in diameter.

During diagnosis, the leak detection pump (LDP) -V144- builds up a pressure of approx. 30 mbar in the EVAP system. The pump will switch OFF when the correct pressure is obtained. If pressure falls below a certain value, the pump will switch ON again. The On Board Diagnostic (OBD) monitors the time between the switched ON periods and if it is too short, will register a malfunction in the Diagnostic Trouble Code (DTC) memory.

Vehicles from 06.99

These vehicles include the latest EVAP system generation with an On board Refueling Vapor Recovery (ORVR) system. The ORVR system is a type of Evaporative Emission (EVAP) control system required for new vehicles. When refueling, vapor in the fuel tank is displaced by incoming fuel, and this fuel vapor, which used to be vented to the atmosphere, is now recovered. The ORVR system requires a large EVAP canister, large vent lines and a new breather valve.