Evaporative Emissions System: Description and Operation

Evaporative Emissions (EVAP) System

Function description of leak diagnostic
The EVAP system (incl. fuel tank) is equipped with a leak diagnostic that detects leaks (improper seal) in the system.

The diagnostic is based on pressure characteristics and is intended to detect leaks with diameters greater than 1mm.

During diagnostic, the Leak Detection Pump (LDP) -V144- generates a positive pressure of approx. 30 bar in fuel system. Pump is switched off once pressure is reached. If pressure falls below a specified value, pump is switched on again. On Board Diagnostic monitors switch condition and stores a DTC in DTC memory if intervals are too short.


NOTE:
- During this work step, the diagnostic pump can start repeated diagnostic procedures until the specified value is obtained, depending on how much fuel is in fuel tank.
- Check sealing cap of fuel tank to make sure it is securely threaded in and that the sealing ring is not damaged.
- All hose connections are secured with spring-type clamps or tensioning clamps.
- Always replace tensioning clamps with spring-type clamps.
- VAS5024 assembly tool or VAG1921 pliers are recommended for installing spring clips.