Oxygen Sensor: Description and Operation

Heated Oxygen Sensor:

The Heated Exhaust Gas Oxygen (HEGO) sensor is threaded into the exhaust manifold with a sampling tip extending into the exhaust stream.
The sensor is a zirconium dioxide ceramic thimble with platinum surface electrodes. The ceramic thimble is oxygen ion conductive and generates voltage due to the oxygen content difference between the atmosphere and the exhaust gas. The sensor will generate a voltage signal between 0 volts (lean condition) and 1.1 volts (rich condition). The Electronic Control Assembly (ECA) reads this signal to achieve an air/fuel ratio of 14.7:1 when operating in CLOSED LOOP.
The HEGO sensor must operate above 600°F. To quickly heat up the sensor, a heating element is incorporated into the sensor.
The HEGO sensor will also set a fault code when the ECA determines the output signal to be out of the normal operating range.