DME 7.8

P0442

97 Fuel Tank Ventilation System (Micro-Leak) - Below Limit

Diagnosis conditions
- Oxygen sensing system active
- Engine running
- Vehicle speed = 0 km/h
- Intake air temperature between 5 °C and 60 °C
- Altitude correction factor greater than 0.75
- Battery positive voltage greater than 11 V
- Engine load less than 30%
- EVAP canister burden less than 3
- Time elapsed after engine start-up greater than 990 seconds or mixture adaptation completed
- No other faults in memory

Possible fault cause
- Tank cap seal
- One or several leaks in fuel tank ventilation system

Diagnosis/troubleshooting

NOTE:
- Fuel tank ventilation diagnosis is initiated with the Porsche System Tester 2 in the "Short test" menu. This reduces the time elapsed after engine start-up to 30 seconds.
- The EVAP canister purge valve is very sensitive to contamination. If the lines to the EVAP canister have to be detached, the outside of the canister must be cleaned beforehand.

Part 1:

Figure:

NOTE:
- Do not produce a vacuum of more than 100 mbar, as otherwise the vacuum will cause the shutoff valve to open.
- If no vacuum can be built up, replace the shutoff valve.
- Coat the sealing ring of the new shutoff valve with tyre fitting lubricant prior to installation.
- The shutoff valve can only be installed in one position: with the electrical connection facing upwards.

Part 2:

NOTE:
- If no leaks are found, a gauge pressure of max. 100 mbar (0.1 bar) can be generated at the EVAP canister at the connection to the tank using special tool 9160/1, in order to increase the escape of fuel vapours.
- Before detaching the ventilation lines from the EVAP canister, clean the area around the connections. Dirt must not be allowed to get into the connectors.

Part 3:

Figure: