911 Carrera 4 Cabriolet (996) F6-3.4L (1999)
Oxygen Sensor Heater Monitoring
For proper function of the 02-sensor, the sensor element must be heated. A none functioning heater delays the sensor's readiness for closed loop control
and thus influences emissions.
The monitoring function measures both, the sensor heater current (voltage drop across a shunt) and the heater voltage (heater supply voltage) to calculate
the sensor-heater resistance.
The monitoring function is activated continuously, if the heater has been stabilized, and the current falls to a static value
Therefore the resistance of the 02-sensor heaters, with the help of a shunt both before and after the catalyst are measured and an additional right/left
diagnosis is realized.
Circuitry for heater controlling and heater current measuring
characteristics: