Evaporative System Testing

Evaporative emissions system, checking, Vehicles up to 1996

Special tools and equipment






Hand vacuum pump VAG 1390 (or US8026 hand vacuum pump)






Vacuum tester VAG 1368

Test conditions

Ignition switched off


Checking EVAP canister

- Remove air cleaner.






- Disconnect purge hose -1- from EVAP canister purge regulator valve -6- and install VAG 1390 (or US8026 hand vacuum pump) to hose.
- Disconnect breather hose -3- (from fuel tank) at EVAP canister and plug port on canister.

- Operate VAG 1390 (or US8026 hand vacuum pump) several times.
Vacuum must not build up

If vacuum builds up:

- Check breather connection -5- on EVAP canister -4- for contamination. Clean as necessary.
- Check EVAP canister purge regulator valve -6- for continuity and replace if necessary.
- Remove plug from canister port.

Checking fuel tank and fuel filler cap

- Remove fuel filler cap.






- Connect VAG 1390 to breather hose -3- from fuel tank (previously removed from EVAP canister -4-).

- Operate VAG 1390 hand vacuum pump several times.
Vacuum must not build up

If vacuum builds up:

- Check gravity valve
- Check line -3- (from fuel tank) for blockage.

If vacuum does not build up:

- Reinstall fuel filler cap.

- Operate VAG 1390 hand vacuum pump several times.
Vacuum must not build up

Note: If the fuel levels are low, it will take much longer to build vacuum, so the pump must be operated at least 20 to 30 times.

If vacuum builds up:

- Replace fuel filler cap.