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What Are Oxygen or O2 Sensors: Their Function & Signs of Failure

Educational  ·  September 10, 2020

What Are Oxygen or O2 Sensors: Their Function & Signs of Failure

It takes thousands of parts to build a car – some parts are big, while others are small, even tiny. Many car parts are critical to the operation of a car, yet we don’t see them or know about them. These are what I like to call the ‘unsung heroes’ of our cars. Without them, we wouldn’t be able to drive our cars at all! One such unsung hero is the oxygen sensor, aka O2 sensor.

On most combustion-engine vehicles today, the oxygen sensor is located somewhere on the passenger side of the car. You can usually find it attached to the exhaust system close to the catalytic converter. As the name suggests, the sensor is a car part with only one purpose: to measure oxygen.

Let’s find out more.

How Does A Car Oxygen Sensor Work?

Oxygen sensors measure oxygen, that’s clear at this point. But does it measure the oxygen content in the cabin, breathed in and out by the occupants? No. What it measures is the amount of oxygen that flows out of the engine through the exhaust system.

Remember that a combustion engine requires air (and the oxygen in it) and fuel in order to function. These two elements must also come in balanced ratios, or else the engine’s efficiency will drop. Measuring how much oxygen comes out through the exhaust system is critical for that balance.

Too much oxygen coming out of an exhaust system might suggest one thing: there's too much oxygen flowing into the engine. Thanks to the O2 sensor, the engine can then make adjustments on how much air it's taking in.

What Happens When the Oxygen Sensor Fails to Work Properly?

Suppose the oxygen sensor isn’t working correctly in your car, what happens then? Well, for starters, the ratio of air and fuel that enters your engine will be incorrect. Perhaps there’ll be too much or too little air taken in by the engine, resulting in an inefficient combustion process. 

So, when do you know that the sensor is failing? Inefficient combustion will only start telling its story when you realise that your fuel consumption is much higher than it was before.

How do you know when your oxygen sensor is bad?

Thankfully, there are other signs and symptoms you can look for when it comes to faulty O2 sensors. Think about it this way. An engine is a well-engineered machine. If all of its parts work correctly, then the engine will operate smoothly and almost quietly.

Once the oxygen sensor becomes faulty and the combustion process is compromised, here are a few common signs you’ll notice:

Can you replace a bad oxygen sensor yourself? 

The answer is yes. 

Assuming that sensor is the cause of the problems you’re facing, you can order the parts online using the parts finder at and do it yourself. You will, however, need to have special tools, such as a special oxygen sensor socket, a car jack and jack stands, and a few other things.

Personally, I prefer to leave some of the more complicated repairs to the experts. Your friends might tell you that mechanics are costly and that you'll save money if you replaced your O2 sensors yourself. To some extent, they're right. But an expert mechanic with the right tools and experience will get the job done quickly and correctly, giving you peace of mind. For me, being able to sleep well at night without wondering whether I've installed the sensor correctly or not is so much more important than the money I pay for my mechanic’s expertise.

Can you drive with a bad oxygen sensor?

Whenever a car part is faulty, you should always get it sorted out as soon as possible. You'll need to replace certain car parts immediately, but you can take your time with certain others. So, under which category does the O2 sensor fall?

Well, you could still drive with a bad oxygen sensor. Your car will still function, even if it doesn't move as smoothly as it usually does. Still, it's not a good idea to delay that repair for too long. Remember: A bad O2 sensor results in an inefficient combustion process. Allow it to happen for too long, and you'll have much bigger engine troubles later.

Whether you decide to replace your oxygen sensor yourself or leave it up to the experts, you can find those parts online along with many others. Just head over to and check out the form for making a Quick Parts Request. Or, you can check out the Directory to find a mechanic near you who can help get that O2 sensor fixed in a jiffy!

By Ray Hasbollah

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