Heated Oxygen Sensor 2 (HO2S2)

Description

The Rear Heated Oxygen Sensor (HO2S 2) is used to monitor the oxygen storage capability of the catalytic converter. Similar to the Front Oxygen Sensor (O2S 1), the HO2S 2 reacts with the oxygen content in the exhaust stream to produce a voltage signal, only after the catalytic converter.

Operation

This voltage ranges from approximately 0.1 volt (high oxygen - lean mixture) to 0.9 volt (low oxygen - rich mixture). Unlike the O2S 1, with a good catalytic converter, the HO2S 2 is normal when its activity appears lazy or inactive. The PCM compares readings from both the front O2S 1 and the HO2S 2 to determine the catalyst efficiency and will illuminate the Malfunction Indicator Lamp (MIL) if this efficiency falls below a calibrated level.