Catalyst Monitor Oxygen Sensors

Catalyst Monitor Oxygen Sensors

Three-way catalytic converters are used to control emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx). The catalyst within the converters promotes a chemical reaction. This reaction oxidizes the HC and CO present in the exhaust gas and converts them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx by converting it to nitrogen. The ECM can monitor this process using the O2 Bank 1 Sensor 1 and O2 Bank 1 Sensor 2 sensors. These sensors produce an output signal which indicates the amount of oxygen present in the exhaust gas entering and leaving the three-way converter. This indicates the catalyst's ability to efficiently convert exhaust gasses. If the catalyst is operating efficiently, the O2 Bank 1 Sensor 1 sensor signals will be more active than the signals produced by the O2 Bank 1 Sensor 2 sensor. The catalyst monitor sensors operate the same way as the fuel control sensors. The sensor's main function is catalyst monitoring, but they also have a limited role in fuel control. If a sensor output indicates a voltage either above or below the 450 mV bias voltage for an extended period of time, the Engine Control Module (ECM) will make a slight adjustment to fuel trim to ensure that fuel delivery is correct for catalyst monitoring.
A problem with the O2 Bank 1 Sensor 1 sensor circuit will set DTC P0131, P0132, P0133 or P0134 depending on the special condition. A problem with the O2 Bank 1 Sensor 2 sensor signal will set DTC P0137, P0138, P0140 or P0141 depending on the special condition. A fault in the heated oxygen sensor (HO2S), heater element or its ignition feed or ground will result in lower oxygen sensor response. This may cause incorrect catalyst monitor diagnostic results.