Oxygen Sensor: Description and Operation

Fig. 21 Oxygen sensor:

Fig. 64 Oxygen Sensor with Internal Heater:

Fig. 8 Oxygen Sensor Voltage:

An oxygen (Lambda) sensor, Fig. 21, Fig. 64, is used to provide more precise control of air/fuel mixtures. This system operates by measuring oxygen content in exhaust gases, as the amount of oxygen remaining in the exhaust gases is directly proportional to the air/fuel ratio of mixtures entering the engine.
The oxygen sensor is made of a ceramic material called zirconium dioxide. The inner and outer surfaces of the ceramic material are coated with a very thin layer of platinum. The outer surface is exposed to the exhaust gasses, while the inner surface is exposed to the outside air.
The difference in the amount of oxygen contacting the inner and outer surfaces of the oxygen sensor creates a pressure differential which results in a voltage signal being generated. The amount of voltage produced is determined by the air/fuel mixture, Fig. 8. A high voltage indicates a rich mixture, and a low voltage indicates a lean mixture.
The oxygen sensors on cars with electronically controlled injection, (CIS-E, CIS-E III, CIS-MOTRONIC), have an internal heating element built into the sensor. These can be easily identified by three wires connecting to the sensor, rather than one as on the K-Lambda systems.