Forenza L4-2.0L (2004)
Oxygen Sensor: Description and Operation
Catalyst Monitor Heated Oxygen Sensors Description
Three-way catalytic converters are used to control emissions of hydrocarbons (HC), carbon monoxide (CO), and Nitrogen Oxide (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 Engine Control Module (ECM) can monitor this
process using the HO2S1 and HO2S2 sensor. 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 HO2S1 sensor signals will be more active than the signals produced by the HO2S2 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 ECM will make a slight adjustment to fuel trim to
ensure that fuel delivery is correct for catalyst monitoring.
A problem with the HO2S1 sensor circuit will set DTC P0131, P0132, P0133 or P0134 depending, on the special condition. A problem with the HO2S2
sensor signal will set DTC P0137, P0138, P0140 or P0141, depending on the special condition.
A fault in the Heated Oxygen Sensor 2 (HO2S2. heater element or its ignition feed or ground will result in lower oxygen sensor response. This may
cause incorrect catalyst monitor diagnostic results.
