Oxygen Sensor: Description and Operation

Fig. 4 Oxygen sensor:

The oxygen sensor, Fig. 4, produces voltage signals when exposed to oxygen in the exhaust gasses. The oxygen content in the exhaust gasses is directly proportional to the air/fuel mixture entering the engine, and the voltage signal produced by the sensor is inversely proportional to the amount of oxygen remaining in the exhaust gasses. The SMEC uses these signals to determine air/fuel mixtures entering the engine.
The oxygen sensor is mounted in the exhaust manifold, and the sensing element must be heated by exhaust gasses before the sensor begins to produce voltage signals. When exhaust gas oxygen content is high (lean mixtures), the sensor produces a low voltage. When oxygen content is low (rich mixtures), the sensor produces a higher voltage.