Evaporative Emissions System: Description and Operation

Evaporative Emissions (EVAP) System

Functional description of leak diagnosis

The EVAP system (including fuel tank) is equipped with a leak diagnostic, the leak diagnostic will detect whether the system is leaking.
The diagnostic operates by pressurizing the system and should detect leaks where the damage exceeds 1 mm (0.040 inch) in diameter.
During the diagnostic the Leak Detection Pump (LDP) -V144- builds up a pressure of approx. 30 mbar (0.44 psi) in the EVAP system. The pump will switch off when the pressure is attained.
When the pressure falls to below a certain figure, the pump will switch on again. The On Board Diagnostic (OBD) monitors the time between the switched on periods and if the time is too short it will register a malfunction in the DTC memory.

Notes:
^ Hose connections are secured with either spring-type or clamp-type clips.
^ Always replace clamp-type clips with screw-type clips.
^ VAG 1921 pliers are recommended when installing spring type clips.

Observe all safety precautions. Technician Safety Information

Observe rules of cleanliness. Vehicle Damage Warnings