How does an oxygen sensor work?

Answer 1

Simply put, an oxygen sensor reacts to oxygen thus creating a voltage as high as 0.9v. The higher the voltage the richer the engine is running. Abnormally high voltage is caused by unburnt oxygen in the system (misfire), abnormally low voltage (vacuum leaks) is a system running with a lack of fuel. An engine running properly will show an upstream (sensor 1) O2 sensor switching from .1 to .9 volts as the computer hunts for the optimal mix or 14.7 parts of air to 1 part of fuel for gasoline engines. The downstream (sensor 2) should show a relatively stable, and lower voltage as these leftover combustion gases are scrubbed through a catalytic converter.
If an oxygen sensor fails, the computer will substitute the O2 signal with a predetermined value. Typically and over rich mixture will be used to protect the engine as damage can occur if running lean, however, prolonged rich mixture can damage the catalytic converter, which can be expensive to replace.
The oxygen sensor is a key component to a fuel injection system. Working in unison with other critical components such as engine coolant temp sensors, air flow sensors, throttle position sensors, these devices prolong engine life, increase fuel efficiency, reduce harmful emissions and have dramatically increased the reliability and ease of use of the modern day engine.