Oxygen (O2) Sensor

The heated oxygen sensor is made from zirconium dioxide, while the inner and outer surfaces are coated with platinum. If fuel mixture is lean (excess oxygen), the oxygen sensor will send a low voltage signal (about 100 millivolts) to the ECM. If fuel mixture is rich (lack of oxygen), the oxygen sensor will send a high voltage signal (about 900 millivolts) to the ECM.