Heated Oxygen Sensor (HO2S)

HO2S is made from zirconium dioxide, while inner and outer surfaces are coated with platinum. If fuel mixture is lean (excess oxygen), HO2S will send a low voltage signal (about 100 millivolts) to ECM. If fuel mixture is rich (lack of oxygen), HO2S will send a high voltage signal (about 900 millivolts) to ECM.