Regal V6-3.8L VIN K (1997)
Oxygen Sensor: Description and Operation
DESCRIPTION
The fuel control Heated Oxygen Sensor (HO2S 1) is mounted in the exhaust manifolds where it can monitor the oxygen content of the exhaust gas
stream. The oxygen present in the exhaust gas reacts with the sensor to produce a voltage output. This voltage should constantly fluctuate from
approximately 100 mV (high oxygen content - lean mixture) to 900 mV (low oxygen content - rich mixture). The heated oxygen sensor voltage can be
monitored with a scan tool. By monitoring the voltage output of the oxygen sensor, the PCM calculates what fuel mixture command to give to the
injectors (lean mixture-low HO2S voltage = rich command, rich mixture-high HO2S voltage = lean command).
The HO2S 1 circuit, if open, should set a DTC P0134 and the scan tool will display a constant voltage between 400 - 500 mV. A constant voltage below
300 mV in the sensor circuit (circuit grounded) should set DTC P0131, while a constant voltage above 800 mV in the circuit should set DTC P0132. A
fault in the HO2S 1 heater circuit should cause DTC P0135 to set. The PCM can also detect HO2S response problems. If the response time of an HO2S
is determined to be too slow, the PCM will store a DTC that indicates degraded HO2S performance.
To control emissions of Hydrocarbons (HO), 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 HO 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
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.
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.
HO2S CONTAMINATION
Contamination of the heated oxygen sensor can result from the use of an inappropriate RTV sealant (not oxygen sensor safe), coolant consumption, or oil
consumption. To check for contamination, remove the HO2S and visually inspect the portion of the sensor exposed to the exhaust stream. If
contaminated, the portion of the sensor exposed to the exhaust stream will have a white powdery coating. Silicon contamination causes a high but false
HO2S signal voltage (rich exhaust indication). The PCM will then reduce the amount of fuel delivered to the engine, causing a severe driveability
problem.
