93 Fuel Tank Ventilation System - Above Limit

P0440

93 Fuel Tank Ventilation System - Above Limit

Function
The fuel vapors from the fuel tank must not escape into the open air. For this reason, the ventilation line of the fuel tank is routed to an evaporative emission filter (or EVAP canister) that retains the fuel vapours. When driving, air is drawn in through the EVAP canister and picks up the accumulated fuel vapours and feeds them to the combustion process.

Diagnosis conditions
- Engine idling
- Vehicle speed = 0 km/h
- Oxygen sensing system active
- Time elapsed after engine start-up > 675 sec.
- No secondary air diagnosis
- Air mass < 30 kg/h
- Engine temperature > 60 °C
- Altitude correction factor > 0.75
- No faults: Throttle position sensor, idle air control, vehicle speed, EVAP canister purge valve output stage, mass air flow sensor, load signal, voltage supply 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.

P0440:

NOTE: 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.

System Overview







Wiring Diagram







Diagnosis Procedure







1 Check installation position of EVAP canister purge valve.







Flow through the EVAP canister purge valve is possible in one direction only. The flow direction is indicated by an arrow on the EVAP canister purge valve. The arrow must point towards the intake manifold.

2 Check triggering of EVAP canister purge valve.
1. Connect Porsche System Tester 2.
2. In the Drive links menu, select EVAP canister purge valve. The EVAP canister purge valve must switch audibly.

3 Check voltage supply and wiring.
1. Remove connector of EVAP canister purge valve.
2. Connect voltmeter (positive) to pin 1 of the connector and to ground.
3. Switch on the ignition.

Display: battery voltage

4. Connect special tool 9637 to wiring harness.
5. Connect ohmmeter to pin III/3 and EVAP canister purge valve connector, pin 2.

Display: 0 - 5 ohms

4 Check EVAP canister purge valve.
1. Disconnect hose from EVAP canister purge valve to intake system at EVAP canister purge valve.
2. Remove connector of EVAP canister purge valve.
3. Connect special tool 9160/1 to EVAP canister purge valve.
4. Generate vacuum of approx. 0.7 bar. The vacuum must not fall below 0.5 bar after 10 minutes.

5 Check hose line between EVAP canister purge valve and air intake system.
1. Undo hose at intake system.
2. Remove connector of EVAP canister purge valve.
3. Connect special tool 9160/1 to hose and generate a vacuum of approx. 0.7 bar. The vacuum must not fall below 0.5 bar after 10 minutes.