5 Symptoms of a Bad Oxygen Sensor (O2), Location & Replacement Cost

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The oxygen sensor, also known as a lambda sensor, is an essential sensor for your car’s performance.

It measures the amount of oxygen in the gases leaving your car through the exhaust. Dr. Gunter Bauman created this sensor in the 1960s when he worked for the Robert Bosch GmbH company.

But like any other mechanical equipment, an oxygen sensor will eventually fail. If it fails, your vehicle will behave abnormally. In this article, we will teach you the common symptoms, the location, and the replacement cost.

5 Symptoms of a Bad Oxygen Sensor

  1. Check Engine Light Illuminates
  2. Poor Mileage
  3. Misfiring Engine
  4. Failed Emission Test
  5. Rough Idle

Here is a more detailed list of the 5 symptoms that may indicate an impending failure of the oxygen sensors.

Check Engine Light Illuminates

Check Engine Light

The sensors are directly connected to the on-board computer of a car. The computer receives data from the sensors and evaluates it. However, if it receives incorrect data or no data at all, it triggers the check engine light on your dashboard.

You may know by now that the check engine light can come on for various reasons; now you know that a faulty oxygen sensor can be one of them.

Poor Mileage

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A bad O2 sensor distorts the tuning of the engine. Not only will the wrong amount of fuel being pumped into the system, but the air-fuel ratio will also be affected. As a result, more or too little fuel is consumed and the mileage is reduced or increased. If you are refueling more frequently, a faulty oxygen sensor could be the reason.

A defective oxygen sensor will not allow the computer to determine the air-fuel ratio for your engine. As a result, the readings are distorted, which affects the performance and the fuel consumption of the car.

Misfiring Engine

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A distorted fuel-air ratio will cause the engine to start to misfire or backfire. If the engine gets too much fuel, it will not be able to burn it all, which will extinguish the spark from the spark plug, resulting in a misfire.

Too lean mixture will also cause misfires when there is no fuel to ignite.

Among other things, the O2 sensor plays an important role in monitoring engine control and fuel supply, so if the sensor is damaged, your general engine condition will deteriorate.

Failed emission test

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A poor or failed oxygen sensor will not only affect your car’s engine performance and fuel efficiency but will also lead to incorrect emission measurements.

As a result, you may get into trouble during an emission test or inspection because the emission tests would fail.

If you know that you car have bad emission results, there is a big chance that your O2 Sensor is bad.

Rough Idle

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Because of the bad air-fuel mixture caused by a bad O2 sensor, it is especially noticeable on idle without load.

For your car to run on idle without stalling, the car needs a perfect air-fuel mixture, and if the oxygen sensor messes up with this, you will notice a rough idle or stalling at idle.

What is an Oxygen Sensor?

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The oxygen sensor is an electronic device installed in your car and measures the amount and concentration of oxygen in the exhausts. It is also known as a lambda sensor.

Advanced automotive technology is capable of producing the most efficient oxygen sensors. The lambda sensor is an essential component of all vehicles manufactured after the 1980s. The main function of the lambda sensor is to collect data on how much oxygen is available for combustion and send it to the engine management system.

The system then uses the data for fuel injection and other purposes.

Oxygen sensors usually do not fail completely, but their efficiency decreases over time.

Location of the Oxygen sensor

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The Oxygen O2 sensor is located in your vehicle’s exhaust system, usually on the exhaust manifold or close to the engine.

There may be several oxygen sensors on your vehicle. These sensors are always located in the exhaust gas flow of your vehicle.

Most cars have one O2 sensor located close to the engine, typically in the exhaust manifold. Some cars have two O2 sensors or more, and the second Oxygen sensor is typically installed behind the catalytic converter.

This helps to monitor catalyst performance by comparing the before and after readings.

Oxygen sensor Replacement Cost

The average oxygen sensor replacement cost is between $100 and $250. The labor costs vary between $50 and $250. You can expect a total of $150 to $500 for an Oxygen O2 Sensor replacement cost.

Based on reports from different areas and vehicle types, we have calculated an average range of the cost to replace the oxygen sensor.

If you plan to replace the oxygen sensor yourself, you would usually only purchase the parts. Remember that any parts on the exhaust pipe can be rusty and difficult to get loose. Some O2 sensors are also located really badly, depending on the car model.

If you use a quality car repair shop, the cost is usually higher than if you have the car repaired by an independent mechanic. If you hire a mechanic to repair your car, he will charge you $50 to $250 to repair the problem in addition to the cost of buying parts.

Because of such large price fluctuations, it is a good idea to do some market research and get several quotes from different mechanics. You can also ask people in your area who have recently replaced or repaired the unit.

Written by: Magnus Sellén

Founder, owner & main author of Mechanic Base. I have been repairing cars for more than 10 years, specialized in advanced diagnostics & troubleshooting. I have also been a drifting driver and mechanic for over 7 years.