On Board Diagnostic

P0446

Activated charcoal filter shutoff valve (function) - Below limit value

Function
To carry out a tank leakage test, the tank vent is closed, but the shutoff valve remains open to enable pressure compensation in the tank system.
The shutoff valve is used to close the purge air line at the activated charcoal filter during the subsequent tank leakage test.
The fault P0446 is set when an excessive vacuum is detected in the tank system over a specified period of time.

Diagnostic conditions:
- Oxygen sensing active
- No secondary air diagnostics
- Mass air flow < 30 kg/h
- Engine running
- Vehicle speed = 0 km/h
- Intake air temperature between 5 °C and 50 °C
- Engine start temperature between 5 °C and 55 °C
- Battery positive voltage > 11 V
- Engine load ≤ 30%
- Correction factor, height > 0.75
- Loading of activated charcoal filter < 3
- Time after engine starts > 990 seconds (16.5 minutes) or mixture adaptation is finished
- No faults entered for:
Throttle potentiometer, idle speed control, Vehicle speed, tank vent, hot film mass air flow meter, power supply, Pressure sensor, shutoff valve, engine temperature

Information: When the tank ventilation diagnostics in the "short test" menu is started using the Porsche System Tester 2, the waiting time is shortened to 30 seconds after the engine starts.

Possible causes of fault:
- Purge air line plugged
- Tank vent stuck in the open state (vacuum continuously enters the tank system from the intake pipe)
- Activated charcoal filter shutoff valve is plugged/stuck in closed state
- Flow resistance of the activated charcoal filter is too high (filter deformed/plugged)
- Pressure sensor closes incorrectly (polarity reversal)

Information: The tank vent is very sensitive to dirt. Before loosening lines or other components, these must be cleaned thoroughly from the outside.

System overview