Oxygen Sensor: Description and Operation

Fig. 4 Exhaust gas oxygen sensor:

This sensor, Fig. 4, is installed in the exhaust manifold and provides information to the ECA as to the oxygen content of the exhaust gases. It monitors the oxygen content of the exhaust gases and generates an output of .6 to 1.0 volt when detecting a rich exhaust gas mixture (absence of oxygen) and less than .2 volts when detecting a lean mixture (presence of oxygen). This constantly changing voltage signal is sent to the ECA for analysis.
The outer surface of the sensor is a threaded steel housing and shell. The sensor body is protected by a shield pressed into the housing where it projects into the exhaust manifold. Exhaust gases contact the sensor body by entering through flutes in the sensor shield. A vent is provided in the shell to allow atmospheric air to enter the inner portion of the sensor body. The sensor connects to the vehicle wiring harness with a connector that is attached to the inner (positive) terminal. The shell is the negative terminal of the sensor and provides the return signal path through the engine block.