Grand Prix V6-191 3.1L VIN M SFI (1998)
Heated Oxygen Sensor: Description and Operation
Catalyst Monitor Heated Oxygen Sensor (HO2S 2)
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.
OPERATION
The PCM has the ability to monitor this process using the (HO2S 1) and the (HO2S 2) heated oxygen sensors. The 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 HO2S 2 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 HO2S 1 signal will be far more active than that produced by the HO2S 2 sensor.
The catalyst monitor sensors operate the same as the fuel control sensors. Although the HO2S 2 sensors main function is catalyst monitoring, it also
plays a limited role in fuel control. If the 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.
SCAN TOOL DIAGNOSIS
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 Catalyst monitor
diagnostic results. A fault in the HO2S 2 heater circuit should cause DTC P0141 to set.
