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.

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Recent Oxygen Sensor Replacement reviews

Excellent Rating


Rating Summary


17 years of experience
1794 reviews
17 years of experience
Toyota 4Runner V6-3.4L - Oxygen Sensor Replacement (Front/Upper/Upstream) - Sammamish, Washington
I am very happy with the service on my 2001 Toyota 4 Runner. Theodor replaced my Oxygen Sensor that was causing my check engine light to be on. He was very fast. I was given a price under what it would have been hsad I taken it to the dealer.
Jeep Liberty - Oxygen Sensor Replacement (Front/Upper/Upstream) - Lynnwood, Washington
Thedore arrived early and was done quickly. He is very knowledgeable vand friendly and highly recommend him.


13 years of experience
511 reviews
13 years of experience
Jeep Wrangler L6-4.0L - Oxygen Sensor Replacement (Front/Upper/Upstream, Rear/Lower/Downstream) - Charlotte, North Carolina
Corey went above and beyond expectations with my appointment. Quality work, very timely but more importantly he took it upon himself to make sure everything was right. definitely recommend and will use in the future.
Honda CR-V - Oxygen Sensor Replacement (Front/Upper/Upstream) - Charlotte, North Carolina
Corey was very knowledgeable and courteous. His work was very good. I would highly recommend him for any mechanic jobs. I was very satisfied.


8 years of experience
191 reviews
8 years of experience
Chevrolet Cruze L4-1.4L Turbo - Oxygen Sensor Replacement (Front/Upper/Upstream) - Saint Louis, Missouri
Very professional and honest! Thought I needed an alternator and turned out to be an O2 sensor. Johnathan went and got the part and was done in no time. Great mechanic! I hope to have him again should another issue surface.
Subaru Legacy - Oxygen Sensor Replacement (Rear/Lower/Downstream) - Saint Louis, Missouri
John was very thorough and completed the maintenance faster than I expected. He was also very familiar with my car already and answered any questions I had.


42 years of experience
519 reviews
42 years of experience
Lexus SC430 V8-4.3L - Oxygen Sensor Replacement (Front/Upper/Upstream) - Spring, Texas
This is the 3rd or 4th time I've had Ron out to work on one of our cars. He is always prompt, friendly, knowledgable and diligent in getting the work done right the first time.
Ford F-150 - Oxygen Sensor Replacement (Front/Upper/Upstream, Rear/Lower/Downstream) - Humble, Texas
Very pleasant experience good mechanic would strongly recommend to others as well as any future work

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