Evaporative Emissions System: Testing and Inspection

Evaporative Emissions (EVAP) System, Leak Checking

Functional description
The evaporative emissions system (including fuel tank) is equipped with a self-checking leak diagnosis capability.

The diagnosis operates by first pressurizing the system and then measuring the leakdown rate between tank pressurizations. A Diagnostic Trouble Code (DTC) is generated when the rate is equivalent to a leak in excess of a 1 mm diameter hole.

During the diagnosis the fuel system diagnostic pump -V144- builds up a pressure of approx. 30 mbar in the activated charcoal filter 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 self-diagnosis monitors the time between the switched on periods and if it is too short it will register a fault in the fault memory.

During the diagnosis, the Leak Detection Pump (LDP) -V144- builds up a pressure of approx. 30 mbar in the canister. The pump will switch off when the preset pressure is attained. When the pressure falls below a certain value, the pump will switch on again. The On Board Diagnostic monitors and compares the time between the switched on periods and, if too short, will store a malfunction in the DTC memory.


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