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What Is an O2 Sensor?

Oct 22, 2021 ·

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A vehicle’s exhaust system is important for many reasons. When a car’s being driven, it produces waste gases that need to be carried away from the engine. The exhaust system plays a key role in managing emissions and ensuring fumes are expelled properly.

Several parts make up this system, including the oxygen sensor, which is often called an O2 sensor. These components work together to communicate with the fuel injection system to help maintain the performance of the vehicle.

Keep reading to find out more about how the O2 sensor works within the exhaust system and why it’s so important.

What Does an O2 Sensor Do?

The O2 sensor is responsible for measuring how much unburned oxygen is in the exhaust. It communicates with your vehicle’s electronic control unit (ECU) to help figure out what the right air-to-fuel ratio should be for the best engine performance.

Through monitoring these oxygen levels, the O2 sensor performs the important role of measuring this mixture so that the fuel injection system can adjust accordingly. O2 sensors can tell the ECU whether a fuel mixture is too lean (meaning there is too much oxygen) or too rich (not enough oxygen).

O2 sensors became mandatory on vehicles starting in 1981, and many vehicles made after 1996 were required to have multiple oxygen sensors. The additional O2 sensors are used to monitor how the catalytic converter is operating.

Where Is the O2 Sensor Located?

The O2 sensor can be found within the exhaust manifold, which is connected to the engine and helps collect emissions. The manifold receives the mixture of air and fuel from engine cylinders.

Warning Signs of a Failing O2 Sensor

O2 sensors don’t require regular maintenance like air filters or oil filters, but over time they can start to wear out. A failing oxygen sensor could lead to the ECU being unable to regulate the proper air-to-fuel ratio, which can cause engine performance issues.

Here are some possible indicators of O2 sensor wear and tear:

  • Decreased gas mileage: A failing oxygen sensor could cause an increased amount of fuel injected into the engine, resulting in significantly lowered fuel economy.
  • Engine misfiring: Rough idling and engine misfiring are common signs that an O2 sensor is failing. Combined with a check engine light, this can be an indicator that you need to have the part checked.
  • Drop in engine power: An air/fuel mixture that isn’t regulated properly can cause performance issues with the engine, including difficulty accelerating or reaching full power. This can be caused by a worn O2 sensor.
  • Rotten egg smell: Excess fuel in the engine can produce the smell of rotten eggs that comes from sulfur. Excess fuel could be due to a failing O2 sensor.

If you notice these symptoms or that your check engine light has come on, it’s important to take your vehicle to get looked at by a trained technician, who can determine the source of the problem.

Get Trained on Exhaust Systems at UTI

You can get hands-on training for the automotive industry when you enroll in UTI’s Automotive Technology program. Through our combination of interactive labs and lectures, you could learn the fundamentals to become an automotive technician.

Courses you take during the program can help teach you to repair and maintain a range of vehicle systems, including the exhaust system and the O2 sensor. These skills can help you when applying for entry-level jobs in the industry.1

Total auto technician employment is expected to be 743,800 by 2031.47 Take advantage of the opportunities and take the first step by requesting more information here.

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1) UTI is an educational institution and cannot guarantee employment or salary.

2) For program outcome information and other disclosures, visit

47) The U.S. Bureau of Labor Statistics projects that total national employment for Automotive Service Technicians and Mechanics will be 743,800 by 2031. See Table 1.2 Employment by detailed occupation, 2021 and projected 2031, U.S. Bureau of Labor Statistics,, viewed October 13, 2022. UTI is an educational institution and cannot guarantee employment or salary.

Universal Technical Institute of Illinois, Inc. is approved by the Division of Private Business and Vocational Schools of the Illinois Board of Higher Education.


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