V90 L6-2.9L VIN 96 B6304S (1998)
Oxygen Sensor: Description and Operation
Function
The heated oxygen sensor (HO2S) only operates above a certain temperature, approx. 285°C (545°F). Normal operating temperature is in the range 350
- 850°C (662 - 1562°F).
The heated oxygen sensor is heated electrically. One terminal is supplied with 12 Volts by the main relay, while a second terminal is connected to the
engine control module (ECM). When this terminal is grounded by the engine control module, a current passes through the PTC resistor in the heated
oxygen sensor.
When the heated oxygen sensor is cold, the value of the PTC resistance is low and the current in the circuit is high. The engine control module pulses the
current initially to prevent damage to the PTC resistor. The resistance increases and the current falls and becomes continuous as temperature rises. The
heating period is short, approx. 30 seconds.
The heated oxygen sensor can be damaged if it is exposed to condensed moisture from the engine while the device is hot.
Heating of the heated oxygen sensor starts immediately the engine is started. When sensor temperature reaches 350°C (662°F) it is maintained at a
constant level until exhaust gas temperature at the front heated oxygen sensor and catalytic converter temperature at the rear heated oxygen sensor are
high. This is to ensure that the temperature around the sensors is high enough to avoid water condensing onto them.
Both heated oxygen sensor terminals are connected to the engine control module.
When the engine is running rich, the oxygen content of the exhaust gases is low or zero. The heated oxygen sensor is then transmitting an output voltage
of approx. 0.9 Volts.
When the engine is running lean, there is an excess of oxygen in the exhaust gases. The output voltage from the heated oxygen sensor almost drops to 0
Volts.
The change from high to low signal level occurs at the ideal (stoichiometric) air/fuel ratio of 14.7 kg air/1 kg fuel.
The engine control module uses the heated oxygen sensor signal to control fuel injection continuously to maintain the ideal value.
