Oxygen Sensor: Description and Operation

Primary Heated Oxygen sensors (Primary HO(2)S)




The primary HO(2)S detects the oxygen content in the exhaust gas and sends signals to the PCM which varies the duration of fuel injection accordingly. To stabilize its output, the sensor has an internal heater. The primary HO(2)S is installed in the exhaust pipe.

By controlling the air fuel ratio with primary HO(2)S and secondary HO(2)S, the deterioration of the primary HO(2)S can be evaluated by its feedback period. When the feedback period exceeds a certain value during stable driving conditions, the sensor is considered deteriorated and the PCM sets a DTC.

Secondary Heated Oxygen sensors (Secondary HO(2)S)




The secondary HO(2)S detects the oxygen content in the exhaust gas downstream of the Three Way Catalytic Converter (TWC) and sends signals to the PCM which varies the duration of fuel injection accordingly. To stabilize its output, the sensor has an internal heater. The secondary HO(2)S is installed in the TWC.