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).

CIRCUIT OPERATION
When the Automatic Shut Down (ASD) relay contacts CLOSE, they connect circuit #4 from the Power Distribution Center (PDC) to circuit A142. Circuit A142 supplies battery voltage to the heated oxygen sensors. The Powertrain Control Module (PCM) controls the ground circuit of ASD relay coil.

Circuit A142 splices to supply voltage for the heater elements in the upstream and downstream heated oxygen sensors. Circuit K41 delivers the signal from the upstream heated oxygen sensor to the PCM. Circuit K41 connects to cavity 30 of the PCM.

Circuit K141 delivers the signal from the down- stream heated oxygen sensor to the PCM. Circuit K141 connects to cavity 51 of the PCM.

The PCM provides a ground for the upstream and downstream heated oxygen sensor signals (circuit K41 and K141) through circuit K4. Circuit K4 connects to pin 43 of the PCM connector and pin 3 the upstream and downstream heated oxygen sensor connectors.

Circuit Z1 provides ground for the upstream heated oxygen sensor. Circuit Z12 provides ground for the downstream heated oxygen sensor.

Helpful Information
Circuit A142 splices to supply voltage to the fuel injectors, ignition coil and generator field.

Circuit K4 also splices to supply ground for the signals from the following:
- Crankshaft position sensor
- Camshaft position sensor
- Throttle position sensor
- Manifold absolute pressure sensor
- Engine coolant temperature sensor
- Knock sensor
- Intake air temperature sensor