Hombre S Regular Cab 4WD V6-4.3L (1999)
Oxygen Sensor: Description and Operation
Due to emissions regulations, the vehicle must enter closed loop as soon as possible. By heating the individual oxygen sensors, they reach their activation
temperature sooner than those without heaters. Once an oxygen sensor reaches its activation temperature, the sensor is able to monitor the oxygen
content of the exhaust more accurately. The vehicle operates in closed loop status once activation temperature is reached. Thus, the VCM's Fuel trim
corrections reduce the vehicle's total emissions. Vehicles produce less emissions when they are in closed loop than open loop.
The Heated Oxygen Sensors are mounted in the exhaust system where they 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 VCM calculates what fuel mixture command to give to the injectors based upon voltage output of the oxygen sensor, (lean mixture - low HO2S
voltage = rich command, rich mixture - high HO2S voltage = lean command). The heated oxygen sensor voltage can be monitored with a scan tool.
Depending upon the configuration of the vehicle's exhaust system, the number of oxygen sensors may vary. The pre-catalyst (HO2S Bank 1 Sensor 1 and
Bank 2 Sensor 1) oxygen sensors are positioned between the exhaust manifold and catalytic converter. The post-catalyst (HO2S Bank 1 Sensor 2, Bank 1
Sensor 3, and Bank 2 Sensor 2) oxygen sensors are positioned between the Catalytic Converter and muffler.
The exhaust Heated Oxygen Sensor (HO2S 1) is mounted in the exhaust manifold where it can monitor the oxygen content of the exhaust gas stream.
Heated Oxygen Sensors (HO2S) - 1
The oxygen content in the exhaust reacts with the sensor to produce 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 heated oxygen sensor, the VCM calculates what fuel mixture command to give to the injector (lean mixture-low
HO2S 1 voltage=rich command, rich mixture - high HO2S 1 voltage=lean command).
The heated oxygen sensor circuit, if open, should set a DTC P0134 and the Scan tool will display a
constant voltage between 350 - 550 mV. A constant voltage below 250 mV in the sensor circuit should set
DTC P0131, while a constant voltage above 750 mV in the circuit should set DTC P0132. DTC P0131 and DTC P0132 could also be set as a result of
fuel system problems.
Heated Oxygen Sensors (HO2S) - 2 / Catalyst Monitoring
In order 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 VCM has the capability to monitor this process using HO2S 2. HO2S 2, located in the exhaust stream past the three- way catalytic converter,
produces an output signal which indicates the oxygen storage capacity of the catalyst; this in turn indicates the catalyst's ability to convert exhaust
emissions effectively. A problem with the HO2S 2 electrical circuits should set DTC P0137, P0138 or P0140, depending on the specific condition.
If the catalyst is functioning correctly, the HO2S 2 signal will be far less active than that produced by HO2S 1. If a problem exists which causes the
VCM to detect excessive HO2S 2 activity outside of an acceptable range for an extended period of time, the VCM will set DTC P0420, indicating that
the three- way catalytic converter's oxygen storage capacity is below a threshold considered acceptable.
