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What’s an O2 Sensor, and Why Should You Care?

O2 sensors are oxygen sensors. As the name implies, it senses the amount of oxygen that’s in a mixture of gas or liquid, such as the exhaust that might come out of your car. Learn more about O2 sensors below, including when to visit an auto repair shop for issues.

What Cars Have Oxygen Sensors, and Where Are They Located?

All cars that were manufactured after around 1980 contain at least one oxygen sensor. Typically, the O2 sensors are located in front of the catalytic converter and in the exhaust manifold of vehicles. Depending on the type and year of your vehicle, you may have between two and four oxygen sensors. The bulk of modern cars typically have four.

The Purpose of Oxygen Sensors

Oxygen sensors measure the ratio of oxygen to other elements within your vehicle’s emissions. If the ratio is outside of the normal expected range for a well-performing engine, the O2 sensor cause the check engine light or another dashboard indicator to come on. O2 sensors also offer feedback to the engine about the oxygen ratio, which can help the engine expend fuel in the most efficient manner possible given the mixture of gas you currently have in the car.

Why Can’t You Ignore O2 Sensors?

In most cases, when the O2 sensor has an issue, the check engine light goes off on your dashboard. But your vehicle is still operable. So, why can’t you ignore the O2 sensor and keep driving until something stops you? There are a number of reasons to visit a car repair shop when O2 sensors fail, including those below.

  • If your oxygen sensor really isn’t functioning, then your vehicle isn’t performing to maximum capability. Your engine could be pushing the wrong amount of fuel based on what mixture of gasoline is currently in the tank. At best, that could lead to lower efficiency when it comes to mileage per hour. At worst, it could lead to a polluted engine and eventually larger problems with the mechanics of your car. 
  • An O2 sensor code could interfere with safety systems. In some vehicles, when the check engine light comes on, certain other systems stop working automatically. For example, in some Toyota 4Runners, the check engine light often shows up along with the TRAC OFF and VSC OFF indicators. That can make your vehicle more difficult to drive. 
  • A faulty O2 sensor could impact your next vehicle inspection. In states with emissions laws, an O2 sensor that doesn’t work or that’s throwing a code can cause you to fail an inspection. That’s because it indicates that something could be wrong with your emissions or that your emissions aren’t being properly regulated by the vehicle itself. If you show up for inspection with a faulty O2 sensor, you’ll likely have to replace it and get the issue fixed before you can get re-inspected and approved for a sticker.

A car repair shop can run a diagnostic on your car to find out exactly what is causing your check engine light to come on. And if it’s the O2 sensor, it’s usually a pretty quick and relatively affordable auto repair job, which means your vehicle will be back on the road and running well again in no time.

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