How does an oxygen sensor work

Each new vehicle and most vehicles delivered after 1980 have an oxygen sensor. The oxygen sensor is one of the emission components that help reduce CO emissions.

The objective of the sensor is to help the motor run the best air to fuel ratio possible.

It just so happens there is a specific proportion of air and fuel that is ideal and that ratio is 14.7:1 “stoichiometric”

The oxygen sensor produces a voltage when the air-fuel ratio is rich “to much fuel”. The computer enters into what you call closed loop when the vehicle is warmed up. Closed loop is when the computer is using the oxygen sensor voltage to control air-fuel ratio.

During closed loop operation when the computer sees the voltage of the o2 sensor go above .5v “rich” it will lean the air fuel ratio down.
When the computer sees the oxygen sensor voltage drop below .5v “lean” the computer will richen the air-fuel mixture. This cycle is repeated over and over again. This is called o2 sensor cross counts.

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