SW1 L4-1.9L SOHC VIN 8 (1996)
Oxygen Sensor: Description and Operation
Front Oxygen Sensor
General Description
The oxygen sensor, mounted in the exhaust system, monitors the oxygen content in the exhaust gas stream. The oxygen sensor acts as an electro chemical
cell, or battery, to produce a voltage in response to oxygen in the exhaust stream compared to oxygen content of the atmosphere. A lean mixture (high
oxygen in the exhaust gas) produces a low voltage and a rich mixture (low oxygen content in the exhaust gas) produces a high voltage. The oxygen
content in the exhaust reacts with the oxygen sensor to produce a voltage output. The voltage signal ranges from approximately 100 millivolts (0.1 volt)
for a lean mixture to 900 millivolts (0.9 volt) for a rich mixture.
By monitoring the voltage output of the oxygen sensor, the PCM will know what fuel mixture command is required to the fuel injectors.
The oxygen sensor operates between 275°C (527°F) to 850°C (1562°F).
The oxygen sensor ground is located on the back of the engine block above the starter.
Circuit Operation
The oxygen sensor (02S) consists of a zirconia electrolyte between two platinum plates. When the sensor reaches approximately 318°C (600°F) it
becomes an electrical source that responds to the oxygen content in the exhaust. The PCM produces a bias voltage of approximately 450 millivolts on the
oxygen sensor circuit. When the sensor is cold its internal resistance is extremely high, therefore, the PCM recognizes the bias as an open circuit. As the
sensor warms up, the internal resistance decreases. When the sensor reaches approximately 318°C (600°F), it starts producing a voltage based on the
oxygen content in the exhaust stream. This voltage is used by the PCM to determine a rich or lean oxygen sensor signal and adjusts the fuel mixture
accordingly.
