911 Carrera 4 Cabriolet (996) F6-3.4L (1999)
Evaporative Emissions System: Testing and Inspection
EVAPORATIVE SYSTEM MONITORING
SYSTEM DESCRIPTION
The evaporative system monitoring is realized by way of a pressure test. A canister close valve ( CCV) and a tank pressure sensor are used to close the
system and observe tank pressure.
Monitoring Conditions
The leak test will be conducted when the vehicle is at rest during an idle condition
Monitoring Process
CCV and the purge control valve ( PCV) are closed and the increase in tank pressure from fuel evaporation is stored ( compensation gradient).
Thereafter the CCV and PCV are opened. The CCV will be shut if the PCV has reached its final duty cycle.
Rough Leak Detection
A rough leak is assumed if the negative pressure build-up gradient is below a certain threshold. In this case the PCV is closed and the CCV opened. The
diagnosis is complete.
Small Leak Detection
The PCV will be closed as soon as Ptank = Plimit The gradient of negative pressure decay will be corrected by the above compensation gradient. From
the corrected gradient a leak flow rate will be determined. A small leak is assumed if the leak flow rate is above a certain threshold. The CCV will be
opened and the diagnosis is completed.
MIL Illumination
If either a rough or small leak is detected for 2 diagnosis cycles then a defective evaporative system is assumed and the MIL is illuminated.
Monitoring Structure