Oxygen Sensor: Description and Operation

The oxygen sensor consists of a primary cell with a fixed electrolyte. The electrolyte is ceramic (zirconium dioxide) and temperature-stabilized by the addition of a small quantity of yttrium oxide. The electrolyte is tubular and hollowed out at one end.

To function properly, the catalytic converter requires an air/fuel ratio of precisely 14.7:1.

If the mixture is too weak, the oxygen content in the exhaust gases will increase. The oxygen sensor output voltage will then be about 0.1 V (lambda over 1). The engine control module reacts by extending the injection times.

If the mixture is too rich, the oxygen sensor output voltage will be about 0.9 V (lambda under 1) and the injection pulses are shortened.

Since the working range of the oxygen sensor is between 200°C and 850°C (392°F-1562°F), it is fitted with an electric preheater. Preheating is controlled by the system control module. At high load and high rpm, the exhaust temperature is high and the preheating circuit is shut off.