Firebird V6-3.8L VIN K (1995)
Oxygen Sensor: Description and Operation
Catalyst Monitor Oxygen Sensors
DESCRIPTION
To control emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx), a three-way catalytic converter is used. The
catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas, converting them into
harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen. The PCM has the ability to monitor this
process using the Bank 1 HO2S 2 and the Bank 1 HO2S 3 heated oxygen sensors. The Bank 1 HO2S 2 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 3 sensor produces an
output signal which indicates the oxygen storage capacity of the catalyst; this in turn indicates the catalyst's ability to convert exhaust gases
efficiently. If the catalyst is operating efficiently, the Bank 1 HO2S 2 signal will be far more active than that produced by the Bank 1 HO2S 3
sensor.
OPERATION
The catalyst monitor sensors operate the same as the fuel control sensors. Although the Bank 1 HO2S 2 and Bank 1 HO2S 3 sensors' main
function is catalyst monitoring, they also play a limited role in fuel control. If a sensor output indicates a voltage either above or below the 450
millivolt 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 HO2S 2 signal circuit should set DTC P0137, P0138 or P0140, depending on the specific condition. A fault in the heated
oxygen sensor heater element or its ignition feed or ground will result in slower oxygen sensor response. This may cause erroneous OC monitor
diagnostic results. A fault in the Bank 1 HO2S 2 heater circuit should cause DTC P0141 to set. A fault in the Bank 1 HO2S 3 heater circuit should
cause DTC P0147 to set.
