Oxygen Sensor: Description and Operation

O2 Sensor Cutaway View (Typical):

SENSOR PURPOSE
Powertrain Control Module (PCM) uses input to determine whether to enrich or lean air/fuel mixture, during closed loop operation.

SENSOR OPERATION
The oxygen sensor generates a varying voltage signal dependent upon exhaust gas oxygen content at that point in the exhaust.

- Oxygen sensor voltage signal is produced through a galvanic reaction within the sensors.

Using the oxygen sensor voltage signal as an air/fuel ratio indicator the PCM can tell how well the system is responding to its output signals.

- Changes in the sensor signal occur because the air/fuel ratio is constantly changing.

- When oxygen content is low (rich mixture), the voltage signal will be approximately 1 volt.

- When oxygen content is high (lean mixture), the voltage signal will be low, approximately 0.1 volt.


Closed Loop
During CLOSED LOOP operation, the PCM monitors the signals it receives from the oxygen sensor, and other sensors, and uses these signals to adjust the injector pulse width according to the current driving condition.

Open Loop
During OPEN LOOP operation, the PCM ignores the oxygen sensor's signals, and other sensor's signals, and adjusts injector pulse widths according to preprogrammed specifications in the PCM.

HEATER PURPOSE
Vehicle enters CLOSED LOOP faster, (because sensor reaches operating temperature sooner).

Allows CLOSED LOOP operation during extended idle, (because heater maintains correct operating temperature).