What are the signs and symptoms of an O2 sensor failure?

Updated February 21, 2017

Most people do not pay attention to their O2 sensors until their car begins to exhibit symptoms or the car fails an emissions test. Manufacturers recommend the replacement of O2 sensors every 60,000 to 100,000 miles to keep air pollution rates within state emission standards. It is also a smart idea to monitor the O2 sensor's function to prevent further damage to the vehicle.


The term O2 sensor is a shortened version of oxygen sensor, which explains the main function of the component's design. The sensors detect the amount of oxygen present in emissions and send a reading back to the car's on board computer, which regulates the air/fuel mixture intake into the engine. When the sensor detects little oxygen in the exhaust, the computer commands more air into the engine. If too much oxygen in found in the exhaust, more fuel is added. When oxygen sensors were originally designed and implemented into fuel-injected cars, one sensor was used for monitoring the entire vehicle. Modern cars can have as many as eight sensors.


O2 sensors were added to vehicles in the 1970s and 1980s to reduce the amount of air pollution produced by vehicles on the road. The car's cycling of changing oxygen and petrol mixtures helps to keep the catalytic converter working at peak performance, reducing the amount of hydrocarbon, carbon monoxide and nitrogen released into the air. Because O2 sensors decline slowly over time, many people do not find out that their car's sensors need to be replaced until they fail an emissions test.

Signs and symptoms

An O2 sensor seldom breaks all at once. The sensor gets covered by road debris and oil ash, and over time, frequently relays to the computer that the car needs more fuel than necessary. The most obvious signs that the oxygen sensor is failing are the illumination of the car's dashboard engine indicator light and reduction of fuel economy.


If a car fails an emissions test or the engine light comes on, the problem can be pinpointed by taking the car to a mechanic or car parts shop to have a digital storage oscilloscope (DSO) hooked up to the car's on board computer. The tool will read diagnostic codes stored on the computer and will help to pinpoint the cause.


Car owners can have sensors replaced by a professional mechanic or install them at home. The sensors can be straightforward to replace, though corrosion and rust on the sensor's threading can make them difficult to remove. For severe rust or hard to reach sensors, it is best to take the car to a professional mechanic for replacement.

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About the Author

Lauren Thompson lives in Kansas City, Missouri and works as both a writer and freelancer. Her background is in technical and spec writing for the information technology industry, as well as financial services. She also writes opinion and editorial articles for KCParent and Parents Edge, specializing in entertainment, food and political realms.