Amanda Drago
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When Do I Need to Replace My Car’s Oxygen Sensor?

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An oxygen sensor on the ground
Photo: Hans Haase via CC

Modern cars have an oxygen sensor, which measures the amount of unburned oxygen in the exhaust as it leaves the engine. If there’s too much or too little oxygen present, the engine will adjust accordingly to improve its performance. A malfunctioning oxygen sensor can spell disaster for your engine, so be sure to keep an eye out for the following signs that you need to replace this part.


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Check engine light

When the check engine light comes on, this could mean your engine is experiencing any of a number of issues. The engine could have something as simple as a loose gas cap or a more major issue like a faulty catalytic converter or a bad oxygen sensor. It’s always a good idea to take your car to a service center when you see the check engine light so that the issue can be properly diagnosed and resolved.

Increased fuel consumption

If you need to fill up the gas tank more often than you used to, a bad oxygen sensor may be to blame. Your car can have as much as a 40 percent improvement in fuel economy after replacing the oxygen sensor, so it’s worth having a technician check it if you’re spending too much time at the gas station.

Other signs

A faulty oxygen sensor can also cause your car to stall and the engine to misfire. In addition, when your car is sitting idle, it may feel rougher than usual. Have a mechanic take a look at your engine soon after experiencing these problems, or you could end up stranded on the side of the road.


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An oxygen sensor replacement can cost under $100 or even above $300, depending on the placement of sensors in your vehicle. Luckily, this part can last for tens of thousands of miles, so you may never need to replace it.