Rear Heated Oxygen Sensor

REAR HEATED OXYGEN SENSOR (REAR HO2S)
The rear heated oxygen sensor (Rear HO2S), downstream three way catalyst, monitors the oxygen level in the exhaust gas. This sensor is made of ceramic titania, the electric resistance of which drastically changes at the ideal air/fuel ratio. The output voltage of the sensor, depending on its resistance, is approximately 0 to 2.2 volts.

The Engine Control Module (ECM) supplies the sensor with approximately 2 volts and then measures the output voltage depending on its resistance. The rear heated oxygen sensor is not directly used to control the engine system. It is used only for the on-board diagnosis of three way catalyst.