The Vehicle Lab is reader-supported. If you decide to buy through a link on this page, we may earn an affiliate commission.  Learn More

Bad Oxygen (O2) Sensor Symptoms

Owning a car is great; everyone knows that. A car represents a kind of responsibility to its owner. In order to keep your car in good condition, you have to maintain it properly. What does that actually mean?

Car maintenance is a broad topic. For example, obvious things include cleaning your car as well as checking your oil.

oxygen sensor

Then, there are some more complicated matters that some car owners should leave to a professional mechanic; however, there are some things that every driver can and should pay attention to. Your oxygen sensor is one of those things.

What is an Oxygen Sensor

First things first; for those who aren’t really sure what an oxygen sensor is, let’s briefly explain its purpose. There is an oxygen sensor tip located on the inside of your exhaust pipe; the oxygen sensor observes the percentage of oxygen in the exhaust.

So, there are two potentially problematic cases here:

There is too little oxygen (the mixture is too rich)

There is too much oxygen (the mixture is too lean)

oxygen sensors diagram

Neither of these scenarios is quite good; in either case, the oxygen sensor will send a signal to the Engine Control Unit (ECU) with the message to adjust the amount of fuel that is entering your engine.

So, why is it important to have a correctly working oxygen sensor? Because the wrong mixture of oxygen and gasoline can increase pollutants exiting your exhaust and harm the environment. Moreover, your catalytic converter might end up being damaged, which would result in additional repairs and costs.

Signs of a Failing O2 Sensor

Most drivers easily notice when something changes in the way their car performs; especially those who drive every day. That is a good thing, naturally; noticing a problem from the get-go makes it easier to solve.

Here is the list of typical bad oxygen sensor symptoms that might point to a failing O2 sensor. If you notice any of these while driving your car, it would be advisable to check if your oxygen sensor is functioning properly.

1. Check Engine Light

check engine light

The bright orange “check your engine” light is one of the first signs that you will notice if your oxygen sensor is not performing properly. However, the problem is that this light can have a number of meanings; maybe it’s only pointing to a loose gas cap.

Since it can be ambiguous why this light comes on, it’s best to contact a professional who will look at the issue more closely and determine the root cause.

2. Your Engine Sounds Rough

If you have noticed that your vehicle is running irregularly or that the engine sounds rough, there might be a problem with your oxygen sensor. When the mixture in your car (oxygen and fuel) is too lean or too rich, the engine becomes less efficient.

A bad sensor could easily disrupt some engine functions such as engine timing, the air to fuel ratio, and combustion intervals. That is what causes your engine to sound rough or perform unpredictably.

3. Bad Gas Mileage

As we already mentioned, when the fuel to oxygen ratio is too lean or too rich, your engine becomes less efficient. That affects the fuel consumption. If you notice that you are spending more than usual on fuel, your oxygen sensor might be failing. You will probably perceive a gradual increase in costs since oxygen sensors tend to become less effective over time in most cases.

4. Emission Test Failure

emissions test

The majority of emission test failures stem from a bad oxygen sensor. If you put off replacing your sensor for too long, you might end up paying thousands of dollars to have your car running properly again.Also, an unpleasant smell similar to rotten eggs might appear in your car. Furthermore, a bad oxygen sensor could expose you to carbon monoxide. If you have a faulty oxygen sensor, it is essential that you replace it sooner rather than later.

When to Replace Your Oxygen Sensor

If your car is no more than 15 years old, consider replacing your sensor every 60,000 to 90,000 miles. All oxygen sensors fail over time; they take a lot of wear and tear. Bear in mind that you will benefit a lot from replacing your sensor. Your car will become more eco-friendly, as it will reduce the emission of pollutants in the atmosphere. In addition, your engine will run smoothly.

So, as soon as you see the “check your engine” light, or notice irregular engine idle, poor gas mileage, or smell rotten eggs, give your mechanic a call. It is vital that you don’t ignore bad oxygen sensor symptoms and react as soon as you notice the usual warning signs.

Richard Reed
I've been a General Manager of a moving company and I've also been a Professional Mover for over 30 years. I've driven flat beds, reefers, dropdecks, moving vans, heavy machinery, etc. In my time as a Mover I've driven over 1,000,000 safe miles. My days of moving and driving truck are past me but The Vehicle Lab allows me to share the knowledge I've gained over the past 40 years.

Leave a Reply

Your email address will not be published. Required fields are marked *

Copyright © 2020 is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for website owners to earn advertising fees by advertising and linking to amazon(.com,, .ca etc) and any other website that may be affiliated with Amazon Service LLC Associates Program.

linkedin facebook pinterest youtube rss twitter instagram facebook-blank rss-blank linkedin-blank pinterest youtube twitter instagram