Heated Oxygen Sensor 2 (HO2S 2) Catalyst Monitor

CATALYST DESCRIPTION
To control emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx), a warm-up three-way catalytic converter is used. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas, converting them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen.

CATALYST MONITORING
The PCM uses the Heated Oxygen Sensor 2 (HO2S 2) to monitor the oxygen storage capability of the catalytic converter. Similar to the HO2S 1, 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 .1 volt (high oxygen - lean mixture) to .9 volt (low oxygen - rich mixture). Unlike the HO2S 1, the HO2S 2 is normal when it's activity appears lazy or inactive. The PCM compares readings from both the front HO2S 1 and the HO2S 2 to determine the catalyst efficiency.