Heated Oxygen Sensor (HO2S)

HO2S measures amount of oxygen in exhaust gas. HO2S provides a voltage signal between zero and one volt, which the ECM uses to adjust air/fuel ratio (amount of injection time). Approximately one volt is generated when air/fuel ratio is too rich and approximately zero volts when air/fuel ratio is to lean.

Sensor has a closed-end tube of ceramic Zirconia, coated with platinum. The outer surface of the tube is exposed to exhaust gases. The inner surface is exposed to atmosphere which, when heated in the presence of exhaust gases, produces a varying voltage signal relative to oxygen content of exhaust gases. Ground for heating element is controlled by ECM. One HO2S is used on G20 and 2 HO2S are used on J30 and Q45. ECM controls heater to activate HO2S.