Your car's oxygen (O2) sensors are critical to your performance, emissions, and efficiency. Oxygen sensors always come in pairs in modern vehicles; your car may have two or four sensors, depending on its design. Manufacturers place one sensor upstream of the catalytic converter and another downstream, each providing important data about the efficiency of your vehicle.

While O2 sensors are extremely important to your car's operation, they can also be frustrating. Faulty O2 sensors are a common cause of illuminated check engine lights, leading to plenty of stress and anxiety. Keep reading to learn what to do if your car's check engine light turns on due to a failing oxygen sensor.

Oxygen Sensors, Feedback Loops, and Performance

It's a common misconception that oxygen sensors are only for your car's emissions. While combining data from upstream and downstream sensors is essential for monitoring catalytic converter efficiency, O2 sensors also play an important role in managing your car's air-to-fuel ratio. By monitoring the amount of oxygen in your exhaust stream, O2 sensors can help your car adjust its fuel delivery.

This feedback loop is a key part of modern engine management. Your car reads data from the O2 sensors, adjusts fuel trim up or down based on that data, and then repeats the process. In addition to ensuring maximum efficiency and performance, this approach allows the car to raise diagnostic trouble codes when your engine runs extremely rich (too much fuel) or lean (too much air).

How Faulty O2 Sensors Affect Your Car

Oxygen sensors can trigger several fault codes. The specific fault codes on your car will usually help narrow down the problem with the sensor and point to the affected sensor location. However, when an oxygen sensor fails, your car may raise additional diagnostic trouble codes (DTCs). These codes usually point to fuel trim problems, such as lean or rich running conditions.

A failing O2 may cause your car to fall back on "safe" fuel trims, which may not initially affect drivability. Still, most cars will require some fuel trim adjustment over time. Since your car can't make these adjustments without data from the O2 sensors, you'll likely experience reduced performance, poor fuel economy, and rough idling as time goes on.

When to Replace Your O2 Sensors

In general, it is unnecessary to replace O2 sensors as preventative maintenance. These parts can last for a long time, so trying to guess when they might fail will likely lead to wasted money. On the other hand, you shouldn't ignore a DTC pointing to a faulty O2 sensor. Even if you aren't noticing any other symptoms, missing fuel trim data can still cause your car to run poorly or even suffer additional damage.

Since O2 sensors are relatively cheap and often easy to replace, delaying this important repair will likely be more expensive over the long run. An O2 sensor code isn't a critical problem that requires you to pull off the road immediately, but it's an issue you should address as soon as possible.

Contact an auto repair shop to learn more.