Rodeo LS 4WD V6-3.2L (1998)
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 HO2S 2 and the Bank 2 HO2S 2 heated oxygen sensors. The
Bank 1 HO2S 1 and the Bank 2 HO2S 1 sensors produce 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 and the Bank 2 H02S 2 sensors produce 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 H02S 1 and the Bank 2 H02S 1 signals will be more active than the signals produced by the Bank 1 H02S 2 and the Bank 2
H02S 2 sensors.
The catalyst monitor sensors operate the same as the fuel control sensors. The Bank 1 H02S 2 and the Bank 2 H02S 2 sensors' 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 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 H02S 2 signal circuit will set DTC P0137, P0138, or P0140, depending on the specific condition. A problem with the
Bank 2 HO2S 2 signal circuit will set DTC P0157, P0158, or P0160 depending on the specific condition. A fault in the heated oxygen sensor
heater element or its ignition feed 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)
(4) Bank 2 Sensor 1 (Fuel Control)
(5) Bank 2 Sensor 2 (Catalyst Monitor)
