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

P0442

Fuel Tank Ventilation System (Micro-leak) - Below Lower Limit

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.
At a particular vacuum, the EVAP canister purge valve is closed. The system is now sealed. The time it takes for the vacuum to disappear establishes whether or not there are leaks in the system.

Diagnosis conditions
- Oxygen sensing system active.
- No secondary air.
- No secondary air diagnosis.
- Air mass [<] 30 kg/h.
- Idle speed.
- Vehicle speed = 0 km/h.
- Intake air temperature between -12°C and 60 °C.
- Battery voltage [>] 11 V.
- Engine load [<] 2.4 ms.
- The vehicle must not be at an altitude of above 2448 m.
- Time elapsed after engine start-up [>] 1000 sec.
- No faults: Throttle position sensor, idle air control, load sensing, misfire detection, vehicle speed, EVAP canister purge valve, idle air control valve, mass air flow sensor, voltage supply, pressure sensor, shutoff valve and engine temperature.

P0442:

System Overview







Diagnosis Procedure







1 Check tightness of shutoff valve.







1. Remove front right-hand wheel housing liner.
2. Detach connector of shutoff valve.
3. Detach ventilation line of shutoff valve.
4. Connect shutoff valve to the battery or a separate power supply unit via special tool V.A.G. 1315A/1.

NOTE: Do not actuate the shutoff valve for more than 5 minutes (overload).

5. Connect special tool 9160/1 to EVAP canister.
6. Using special tool 9160/1, produce 100 mbar (0.1 bar) of vacuum.

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.

NOTE:
- Coat the sealing ring of the new shutoff valve with tire fitting lubricant prior to installation.
- The shutoff valve can only be installed in one position: with the electrical connection facing upwards.

2 Check ventilation lines for leaks.





Check the tank system for leaks using an HC tester. To do so, hold the connecting hose of the the HC tester in the spot to be tested. In the case of a leak, the display of the HC tester increases to above 1000 ppm. Values below 50 ppm indicate no leaks.
To test the ventilation lines, guide the connecting hose slowly along them.

Check the following locations:
1. Tank cap
2. Line connections to EVAP canister
3. EVAP canister







4. Line connection to fuel tank sender unit
5. Pressure sensor
6. Opening of fuel filler neck into tank







7. Line connection of EVAP canister purge valve
8. Ventilation lines:
a. from EVAP canister to operating purge valve
b. from operating purge valve to tank
c from EVAP canister to EVAP canister purge valve

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 vapors.

3 Check tightness of EVAP canister purge valve.







NOTE: 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.

1. Detach the ventilation line to the EVAP canister purge valve from the EVAP canister (protective cap).
2. 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.