How an Oxygen Sensor Works in Automobiles

Oxygen Sensors Basics

An oxygen sensor or O2 sensor is an electronic device that measures the amount of oxygen in exhaust gases in modern internal combustion vehicles and other applications.  The oxygen sensor monitors the difference between the oxygen content in the exhaust gases and the outside air and generates a voltage accordingly.  This voltage data is sent to the vehicles computer or ECU (Engine Control Unit).  The ECU uses this data in conjunction with data from other sensors to monitor how the car is running and make adjustments to the fuel air ratio to give optimal power, fuel economy and emissions control.

 How and Oxygen Sensor Works

The adjustments made by the ECU strive to maintain the car running as close to a fuel air ration of 14.7:1, the stoichiometric ratio at which complete combustion occurs.  When an engine is running rich, more fuel is present than indicated by the ratio and a lack of oxygen can be detected in the exhaust; when the engine is running lean, there is less fuel present and high oxygen levels can be detected in the exhaust

Oxygen Sensor Failure

A problem with the oxygen sensor can cause the vehicle to run poorly, have a loss of power and lead to failure of other components if not corrected.  When an oxygen sensor has failed the Check Engine Light (CEL) will usually be set indicating the car needs maintenance or repairs. The mechanic or owner can then read the OBDII code present in the cars computer with a diagnostic scan tool, this code can help identify the source of the problem.  Vehicles will not usually pass inspection that have a faulty Oxygen Sensor

This article describes detecting and replacing a failing Oxygen Sensor on a 1998 Honda Accord.