Evaporative Emissions System: Description and Operation

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.

This diagnostic 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 fuel system Leak Detection Pump -V144- builds up a pressure of approx. 30 mbar in the EVAP system. The pump will switch OFF when correct pressure is obtained. If pressure falls below a certain value, the pump will switch ON again. The On Board Diagnostic monitors the time between the switched ON periods and if it is too short, will register a malfunction in the Diagnostic Trouble Code memory.


NOTE:
- Production hose connections are secured with either spring or clamp type clips.
- When replacing an existing clip, always use the spring-type.
- VAS 5024 or V.A.G 1921 pliers are recommended for installing spring clips.


Observe safety precautions.
Observe Rules for cleanliness.
Evaporative (EVAP) emissions system, overview.