Q: Where Is the O2 Sensor Located?

Oxygen sensors O2 sensors will always be located in the exhaust system. Their function is to sense how much oxygen remains in the exhaust that is flowing out of the engine, and report that information to the vehicle’s engine control computer.

This information is then used to help with accurate fuel delivery to the engine under various driving conditions. Your vehicle’s main computer, the powertrain control module, monitors operation of the O2 sensors. If a problem is noted, the Check Engine Light will illuminate and a diagnostic trouble code will be stored in the PCM’s memory to assist a technician with the diagnostic process.

A couple helpful tips to assist in locating O2 sensors:

• Vehicles built after 1996 will have at least two O2 sensors
  
• 4 cylinder engines will have two oxygen sensors
  
• V-6 and V-8 engines will usually have 3 or 4 oxygen sensors
  
• The sensors will have 1-4 wires on them
  
• The front sensor(s) will be located under the hood, on the exhaust, very close to the engine
  
• The rear one(s) will be located under the vehicle, directly after the catalytic convertor
  

The sensor(s) close to the engine are sometimes called “pre-cat”, being located before the catalytic convertor. This O2 sensor provides information about oxygen content in the exhaust before it is treated by the catalytic convertor. The O2 sensor located after the catalytic convertor is referred to as “post-cat” and provides data about oxygen content after the exhaust has been treated by the catalytic convertor.

When replacing O2 sensors that have been diagnosed as faulty, it is strongly recommended to obtain original equipment brand sensors. They are designed and calibrated to work with your vehicle’s computer. If you have a V6 or V8 engine, replace sensors on both sides at the same time for best results.