Oxygen Sensor: Description and Operation

O2 Sensor Cutaway View (Typical):

LOCATION

The heated oxygen sensors are located in each exhaust manifold in front of the catalytic converter.

FUNCTION

This vehicle uses two oxygen sensors. The 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.