Oxygen (O2) Sensor
Two O2 sensors are mounted in exhaust system where they monitor oxygen content in exhaust stream. There is a sensor mounted in each exhaust manifold. An O2 sensor acts like a battery because it creates its own signal voltage once it reaches operating temperature. This voltage is produced when oxygen content in exhaust stream is different than oxygen content in atmosphere. A lean condition (high oxygen content in exhaust) will produce a low voltage (near 0 volt) and a rich condition (low oxygen content in exhaust) will produce a high voltage (near one volt). The PCM provides a reference signal voltage (0.45 volt) and a ground to sensor. The PCM reference voltage is necessary because O2 sensors do not provide there own voltage until they reach operating temperature. See Fig 1 .
The Northstar O2 sensors also incorporate a heating element inside of sensor housing. This heating element is energized with ignition "ON" and allows sensors to reach operating temperatures quickly. The PCM can then use O2 sensor information sooner after engine start-up.
The PCM uses oxygen sensor information during "Closed Loop" operation to constantly adjust fuel control to reduce exhaust emissions. Because Northstar O2 sensors provide information sooner after engine start-up, exhaust emissions are reduced. Faulty O2 sensors will cause various driveability conditions and should set a PCM Trouble Code.