On-Board Diagnosis System II - Volkswagen Technical Site

System Components (Gasoline Engine)
Diagnosis of a minor leak
The test phase starts after the fuel system
diagnosis pump in the tank system has built up
an overpressure. The drop in overpressure is
monitored at the same time.
The larger the leak, the quicker the succession of
diagnosis pump delivery periods. This indicates a
possible leak and the size of this leak.
A reed switch is coupled with a membrane in the
fuel system diagnosis pump.
If the pressure in the tank system drops, the position
of the membrane changes. If the pressure
drops below a defined value, the reed switch
closes and the pump increases the pressure
again until the reed switch is reopened by the
membrane.
Tank system
tight
Tank system
minor leak
P
P
1
t
1
t
Leak
175_086 175_087
P = pressure, t = time
40