Fuel Tank Ventilation System (Micro-leak) - Below 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 diagnosis
- Air mass less then 30 kg/h
- Engine running
- Vehicle speed = 0 km/h
- Intake air temperature between 5 锟斤拷C and 50 锟斤拷C
- Engine starting temperature between 5 锟斤拷C and 55 锟斤拷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.
- If the diagnosis does not run, give a short acceleration burst.
P0442
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.