Where Is the O2 Sensor Located?

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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 2 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

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YourMechanic Oxygen Sensor Replacement Service

Average Rating

4.9/5

Number of Reviews

1,126

Rating Summary
1,059
39
7
7
14
1,059
39
7
7
14

Jerome

32 years of experience
153 reviews
Jerome
32 years of experience
Nissan Quest - Oxygen Sensor Replacement (Front/Upper/Upstream) - Bowie, Maryland
Jerome was courteous and competent. The service was excellent. I am very much satisfied with the results of the work.

Michael

14 years of experience
501 reviews
Michael
14 years of experience
Nissan D21 - Oxygen Sensor Replacement (Front/Upper/Upstream) - Atlanta, Georgia
Awsome,he's on time,very detailed,and does his,work,in a timely manner..wish there were more,like him I have used him twice and satisfied both visits.

Jermaine

22 years of experience
15 reviews
Jermaine
22 years of experience
Lexus LS430 - Oxygen Sensor Replacement (Front/Upper/Upstream) - Clarksville, Maryland
Jermaine was super. He did a fantastic job with my car repair. I've already recommended him to some of my friends, and will be pleased to request him in the future.

Breck

18 years of experience
528 reviews
Breck
18 years of experience
Chevrolet K1500 - Oxygen Sensor Replacement (Front/Upper/Upstream, Rear/Lower/Downstream) - Humble, Texas
Breck arrived on time. He was very courteous and professional. Displayed great skills as a mechanic. Perfect job of diagnosing problems/issues and addressing them.

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