Oxygen Sensor: Description and Operation

O2 Sensor Cutaway View (Typical):

PURPOSE
This vehicle uses two oxygen sensors. The Powertrain Control Module (PCM) uses these signals to fine tune air/fuel mixture for each cylinder bank. This is done by varying injector pulse width (ON time).

OPERATION
The oxygen sensor is a voltage generating device. A voltage signal (0-1 volt) is generated by comparing the difference in oxygen content between the exhaust gases and outside air. The higher the difference (rich mixture, low exhaust oxygen content) the higher the voltage generated by the oxygen sensor. Smaller differences (lean mixture, high exhaust oxygen content) result in a lower voltage being generated.

On this engine, pairs of injectors are fired (five pairs with one injector on each cylinder bank). Because of this, the PCM is not able to separately adjust left and right bank fuel injection. The PCM averages reading from both O2 sensors, and injects fuel at a common rate for all ten cylinders.

The oxygen sensor has a heating element that maintains proper oxygen sensor operating temperature at all times. This process allows the vehicle to enter closed loop at an earlier time and to remain in closed loop during the remainder of the operating cycle. The oxygen sensor heating element receives voltage from the fuel pump relay.

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.

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.

CIRCUIT OPERATION
This engine uses two oxygen sensors, one in each exhaust down pipe. When the Powertrain Control Module (PCM) grounds the Automatic Shut Down (ASD) relay, the contacts close and connect circuits A14 and A142. Circuit A142 supplies battery voltage to the heated oxygen sensors.

Circuit K41 delivers the signal from the right heated oxygen sensor to the PCM. Circuit K41 connects to cavity 41 of the PCM.

Circuit K141 delivers the signal from the left heated oxygen sensor to the PCM. Circuit K141 connects to cavity 23 of the PCM. The Powertrain Control Module (PCM) supplies 8 volts to the camshaft position sensor (in distributor) on circuit K7. Circuit K7 connects to cavity 7 of the PCM.

The PCM provides a ground for the heated oxygen sensor signals (circuit K141 and K41) through circuit K4. Circuit K4 connects to cavity 4 of the PCM connector. Circuit Z11 provides a ground for the heater circuit in each sensor.