The purpose of the Oxygen Sensor is to tell the vehicles PCM (computer) how rich and lean the air/fuel mixture is.
A gasoline engine burns gasoline when oxygen is present in the cylinder. There is a particular ratio of air to gasoline. This ratio is 14.7:1 (14.7 gallons of air to 1.0 gallons of fuel.)
If there is less air than the designated ratio, then there will be fuel left over after combustion. This would be called a rich mixture.
If there is more air than the designated ratio, then there is more oxygen. This would be called a lean mixture.
Lean mixtures are extremely harmful for the environment. A lean mixture tends to produce more NOx (nitrogen-oxide) pollutants, and can cause poor performance and even engine damage.
When the mixture is rich, there is unburnt fuel left over and can cause poor fuel economy (which can cost you more money at the pump).
When the vehicle's computer data indicates a problem with either rich or lean mixture, it will cause your MIL to illuminate on your dash to indicate to the driver there is a problem with the vehicles computer control system.
This one of the purposes of your vehicles oxygen sensors, on late model vehicles 1996 and newer the post catalytic convert oxygen sensor also monitors catalytic performance.
John Wallen is currently studying Automotive Technology at the Harrisburg Area Community College York Campus
Name: John Wallen
School District: West York Area High School
Area of Interest: Hanging with friends, working on cars, and playing sports
Plans After High School: Join the Army, and then settle down and have a family.