Metro L4-079 1.3L VIN 2 MFI (2001)
Oxygen Sensor: Description and Operation
Heated Oxygen Sensor 1 (HO2S 1)
General Description
Heated Oxygen Sensor 1 (HO2S 1)
The fuel control heated oxygen sensor 1 (HO2S 1) is mounted in the exhaust pipe below the exhaust manifold. The main function of the fuel control
heated oxygen sensor is to provide the Powertrain Control Module (PCM) with exhaust stream oxygen content information. The exhaust stream oxygen
content information enables the PCM to provide the proper fueling and achieve vehicle emissions that are within the mandated levels.
Operation
Heated Oxygen Sensor 1 (HO2S 1)
The HO2S 1 has a zirconia element with a thin platinum surface coating. The zirconia element generates an electromotive force when a there is a
difference in the concentration of oxygen between its faces. This electromotive force is amplified by the catalytic reaction of the platinum when the
zirconia element temperature rises. The inside of the zirconia element is exposed to the atmosphere (reference air) and the outside of the zirconia element
is exposed to the exhaust gases. The difference in concentration between the inside and the outside of the zirconia element varies with the concentration
of oxygen in the exhaust gases. A large difference in the concentration of oxygen results in about 1 volt of electromotive force. A small difference in the
concentration of oxygen results in a about 0.01 volt of electromotive force.
In order for the HO2S 1 to function properly, the sensor must have a supply of clean reference air. Clean reference air is obtained through the oxygen
sensor pigtail wiring. Any attempt to repair the wires, the connectors, or the terminals of the HO2S 1 pigtail wiring could result in the obstruction of the
reference air. Replace the oxygen sensor if the pigtail wiring, the connector, or the terminals are damaged.
The oxygen sensor heater greatly decreases the amount of time required for the HO2S 1 to become active and begin the closed loop fuel control.
The HO2S 1 voltage should constantly fluctuate from approximately 100 mV (high oxygen content - lean mixture) to 900 mV (low oxygen content - rich
mixture). The PCM calculates what fuel mixture commands to send to the fuel injectors by monitoring the voltage output of the oxygen sensor. The
oxygen sensor voltage can be monitored with a scan tool.
