Heated Oxygen Sensor 2 (HO2S 2) Catalyst Monitor

Rear HO2S:

DESCRIPTION
The Rear Heated Oxygen Sensor (HO2S 2) is used to monitor the oxygen storage capability of the catalytic converter. Similar to the O2S, the HO2S 2 reacts with the oxygen content in the exhaust stream to produce a voltage signal only after the catalytic converter. This voltage ranges from approximately 0.1 volt (high oxygen - lean mixture) to 0.9 volt (low oxygen - rich mixture). Unlike the O2S, the HO2S 2 is normal when it's activity appears lazy or inactive. The PCM compares readings from both the front O2S and the HO2S 2 to determine the catalyst efficiency and will illuminate the MIL if this efficiency falls below a calibrated level.