Rodeo S 2WD L4-2559cc 2.6L SOHC (4ZE1) (1997)
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Oxygen Sensor: Description and Operation
Catalyst Monitor Heated Oxygen Sensors
DESCRIPTION AND OPERATION
Three-way catalytic converters are used to control emissions of hydrocarbons (HO), carbon monoxide (CO), and oxides of nitrogen (NOx). The
catalyst within the converters promotes a chemical reaction. This reaction oxidizes the HO 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 Powertrain Control Module (PCM)
can monitor this process using the Bank 1 Heated Oxygen Sensor (HO2S) 2 heated oxygen sensor. The Bank 1 HO2S 1 sensor produces an output
signal which indicates the amount of oxygen present in the exhaust gas entering the three-way catalytic converter. The Bank 1 HO2S 2 sensor
produces an output signal which indicates the oxygen storage capacity of the catalyst. This indicates the catalyst's ability to efficiently convert
exhaust gases. If the catalyst is operating efficiently, the Bank 1 HO2S 1 signal will be more active than the signal produced by the Bank 1 HO2S
2 sensor.
The catalyst monitor sensors operate the same as the fuel control sensors. The Bank 1 HO2S 2 sensor's main function is catalyst monitoring, but it
also has 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 PCM will make a slight adjustment to fuel trim to ensure that fuel delivery is correct for catalyst monitoring.
A problem with the Bank 1 HO2S 2 signal circuit will set DTC P0137, P0138, or P0140, depending on the specific condition. A fault in the heated
oxygen sensor heater element or its ignition teed or ground will result in lower oxygen sensor response. This may cause incorrect catalyst monitor
diagnostic results.
(1) Bank 1 Sensor 1 (Fuel Control)
(2) Catalytic Converter
(3) Bank 1 Sensor 2 (Catalyst Monitor)
