DME 7.2

P0455
94 Fuel Tank Ventilation System (Major Leak) - Below Limit

P0455
94 Fuel Tank Ventilation System (Major Leak) - Signal Implausible

Function
Fuel tank ventilation diagnosis is employed for detecting leaks in the fuel tank ventilation system. In this process, a pressure test is performed at idle speed and with the vehicle stationary.
The EVAP canister purge valve is opened and the shutoff valve closed. This causes a vacuum to build up in the tank, which is measured by the pressure sensor. If no vacuum builds up, a major leak is present. Diagnosis is then terminated.

Diagnosis conditions
- Oxygen sensing system active
- No secondary air diagnosis
- Air mass < 30 kg/h
- Engine running
- Vehicle speed = 0 km/h
- Intake air temperature between 5 °C and 50 °C
- Engine starting temperature between 5 °C and 55 °C
- Battery voltage > 11 V
- Engine load < 30 %
- Altitude correction factor > 0.75
- EVAP canister burden < 3
- Time elapsed after engine start-up > 990 seconds or mixture adaptation completed
- No faults in: Throttle position sensor, idle air control, vehicle speed, EVAP canister purge valve, mass air flow sensor, voltage supply, pressure sensor, shutoff valve and engine temperature

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.







NOTE: A frozen EVAP canister shutoff valve can lead to this fault.

System Overview:

Diagnosis Procedure - Below Limit:

Diagnosis Procedure - Signal Implausible:

1 Check tank cap.

1. Check whether the tank cap is present.
2. Check whether the tank cap is correctly screwed on.

2 Check ventilation lines at EVAP canister.







1. Remove front right-hand wheel housing liner.
2. Check whether ventilation lines are attached to the EVAP canister.

3 Check ventilation lines at operating purge valve.







1. Remove front right-hand wheel housing liner.
2. Check whether ventilation lines are attached to the operating purge valve.

4 Check ventilation line at tank.







1. Remove battery.
2. Remove battery cover.
3. Check whether ventilation line is attached to the fuel tank sender unit.

5 Check ventilation line at EVAP canister purge valve.







Check whether ventilation line is attached to the EVAP canister purge valve.

6 Check ventilation lines.

Check whether ventilation lines are:
- cracked
- broken
- interrupted


7 Check EVAP canister purge valve.







1. Remove front right-hand wheel housing liner.
2. Clean EVAP canister in the vicinity of the ventilation lines.
3. Detach the ventilation line to the EVAP canister purge valve at the EVAP canister (connection with protective cap).
4. With special tool 9160/1, generate a vacuum of 200 mbar (0.2 bar).

If no vacuum can be built up, replace the EVAP canister purge valve.