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.

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
There are two heated oxygen sensor used on this vehicle. Power for the heated oxygen sensors is supplied on circuit A142 when the contacts in the Automatic Shut Down (ASD) relay are CLOSED. Battery voltage for the contact side is supplied on circuit A14. This circuit is HOT at all times and protected by a fusible link located near the auxiliary jumper post on the left toe box.

Power for the coil side of the ASD relay is supplied on circuit A21. This circuit is HOT when the ignition switch is in the START or RUN position. Ground for the coil side of the relay is controlled by the Powertrain Control Module (PCM)on circuit K51.

When the PCM supplies a ground path for circuit K51 the contacts in the ASD relay CLOSE connecting circuits A14 and A142. Circuit A142 powers the heated oxygen sensors and is double crimped at the ASD relay to supply an ASD relay energized input to the PCM.

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

Circuit K241 delivers the signal from the right heated oxygen sensor to the PCM. Circuit K241 connects to cavity 23 of the PCM connector.

The PCM provides a ground for the left and right heated oxygen sensor signals (circuits K41 and K241) through circuit K4. Circuit K4 connects to cavity 4 of the PCM connector.

Circuit Z12 provides the ground path for the heater circuits in the sensors.