Catalyst Monitor Heated Oxygen Sensor (HO2S 2)

A 3-Way Catalytic Converter (TWC) is used In order to control the emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides Of Nitrogen (NOx). The catalyst within the converter promotes a chemical reaction that oxidizes the HC and the CO that are present in the exhaust gases, converting the gases into harmless water vapor and carbon dioxide. The catalyst also reduces and converts the NOx into nitrogen. The ECM monitors this process by using the HO2S 1 and the HO2S 2. The HO2S 1 produces an output signal that indicates how much oxygen is present in the exhaust gas entering the TWC. The HO2S 2 produces an output signal that indicates the oxygen storage capacity of the catalyst. The HO2S 2 signal is thus an indicator of the catalysts ability to convert the exhaust gases efficiently.

In addition to the catalyst monitoring, the HO2S 2 has a limited role in controlling the fuel delivery. If the HO2S 2 signal indicates a high oxygen content or a low oxygen content for an extended period of time while in a Closed Loop operation, the ECM will adjust the fuel delivery slightly in order to compensate for this condition.

If the oxygen sensor pigtail wiring, the connector, or the terminal are damaged, the entire oxygen sensor assembly must be replaced. DO NOT attempt to repair the wiring, the connector, or the terminals. The sensors must have a clean air reference in order to function properly. This clean air reference is obtained by way of the oxygen sensor wires. Attempting to repair the wires, the connectors, or the terminals can result in the obstruction of the air reference and degrade the oxygen sensor performance.