Volkswagen Passat 1995 Official Factory Repair Manual page 2041

EVAP canister system
http://ebahn.bentleypublishers.com/vw/servlet/Display?action=Goto&type=repair&id=VW.B4.FU08.20.2
If no vacuum builds up:
- Screw fuel filler cap on fuel filler tube.
- Operate vacuum pump several times.
There must be no vacuum building up.
Note:
At a low fuel level in fuel tank, hand vacuum
pump must be operated at least 20 to 30 times.
If vacuum builds up:
- Replace fuel filler cap for fuel filler tube.
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