Signs of a Bad o2 Sensor: 8 Causes you must know

Do you know what an oxygen sensor is and what is its purpose? If not, don’t worry. We are here for you to provide any kind of information you want. Let us first tell you that the purpose of an oxygen sensor is to measure the level of oxygen from the residual exhaust gases that are emitted from the engine of your vehicle.

We can say that this sensor is responsible for sending real-time data regarding the amount of unburnt oxygen in your vehicle’s exhaust system to the computer of its engine for determining the accurate air-to-fuel ratio for your car’s engine.

So, if your vehicle has a bad oxygen sensor, you will face air-to-fuel problems that result in fuel combustion inefficiencies. The performance of your engine also becomes weak due to a bad oxygen sensor. Now, you must be thinking about what a bad O2 sensor looks like and how you know you need to change it.

In this guide, we have explained what are the common signs that tell you about the inefficiency of your oxygen sensor. It means these signs indicate the presence of a bad sensor in your vehicle which needs to be replaced as soon as possible.

See More: what to do after Replacing Camshaft Sensor 

Working of an Oxygen Sensor

Before explaining the signs of a bad O2 sensor, let us first discuss the working of this sensor. We know that the internal combustion engine of a car or any other vehicle produces exhaust gases when the mixture of fuel and air ignites in the cylinders. Let us tell you that there are a lot of elements present in these gases where these elements may include oxygen and carbon.

The oxygen sensor works by keeping the track of the oxygen level in the exhaust gases of your vehicle when they leave the engine. This oxygen is not broken down or burnt during the combustion of air and fuel. This sensor detects the amount of fuel that is being burnt by the engine.

Signs of a Bad Oxygen Sensor

There are different signs that are displayed to you when you have a bad oxygen sensor in your vehicle. You need a hawk’s eye to see these signs. Some of these signs are easy to detect so it would be best if you take your vehicle to an expert mechanic to install a new oxygen sensor and protect your vehicle.

Now, let’s come to our major topic and discuss some signs of a bad oxygen sensor:

1. Engine Light Turns On

When there is an issue with your oxygen sensor, you will see the engine light present on your dashboard is turned on. The major purpose of this light is to show that there is an issue with your engine or any of its parts that need to be fixed immediately to avoid any future problems.

You must be thinking what would be the link of an oxygen sensor with the engine light. Being curious is obvious. Let us tell you that when the oxygen sensor stops working, it does not determine the problem, if there is any, with the combustion system of your vehicle.

When this problem will not be detected and fixed timely, the performance of your engine will be affected automatically. It in turn will result in turning on the engine light present in your car. So, it is recommended that you keep in touch with your mechanic and get your vehicle checked regularly to prevent any future problems.

2. Abnormal Fuel Consumption

It is common that when the oxygen sensor is not working, you will surely face bad fuel economy. Plus, the consumption of abnormal fuel also increases when you do not detect the presence of oxygen that is not burnt. No doubt, this gas is hazardous to your health and can also cause lung problems.

Do you want to affect your health? Do you like to damage your engine and affect its performance? Surely not! Who would like to do this, right? Then why don’t you take care of your vehicle and get its different parts checked regularly? No doubt, it will cost you some money but it will save you from future problems that could cost you a lot of money.

Let us tell you that when the fuel is either too lean or too rich, the efficiency of the engine fuel combustion is lost. You should know that the oxygen sensors do not have a long life, that’s why they get damaged easily.

You should know that when the consumption of abnormal fuel is started by your vehicle, you will notice a smell like a foul egg. This smell is produced when the fuel burns because of the production of nitrogen and sulfur residue. You may also notice black smoke coming out of the exhaust system. It is because of low fuel economy.

3. Rough Idling

When the oxygen sensor of your vehicle starts deteriorating, you will see that your vehicle is misfiring frequently. You will also note that your car or any other vehicle is running irregularly and roughly, especially when idling. The problem of failed oxygen sensors results in different issues like stalling, engine hesitation, and power loss especially when you start your car.

Let’s clear the meaning of rough idling. A rough idling engine can be defined as an engine that is not able to run steady when your car is stopped or parked. For an idle engine, the normal RPM is under 1000 but if it exceeds 2000, it means you are suffering from the problem of rough idling.

In this situation, it will become difficult for the engine to manage the engine timing. Moreover, the functioning of the engine is also affected badly. The bad sensor lets the engine run irregularly and roughly.

4. Weak Performance of Engine

When you see that the performance of your engine is not like before and you are not enjoying the smooth ride of your car, it means there is an issue with the engine processes. As we know, there is a relation between the engine processes and the oxygen sensors so the engine processes are affected badly due to bad oxygen sensors.

The performance of your vehicle’s engine becomes weakened. Plus, we will see that the air to fuel ratio is also not balanced which in turn affects your vehicle’s performance. You will find difficulty in starting your car and running it. Plus, you may also notice loud noise coming from your vehicle.

5. Failure of Emission Tests

The emission tests will keep failing if there is an issue with your vehicle’s oxygen sensor. You must be wondering what an emission test is. Let us tell you that some states and countries have the rule of getting the vehicles to go through emission tests. The purpose of this test is to control environmental pollution.

So, if there will be an issue with your oxygen sensor, it will be detected in this emission test. Failure of this test shows that there is a problem with your control system and the oxygen sensor. It is recommended that you get your vehicle checked by a professional.

The failure of this test is not only because of a bad oxygen sensor but there might also be some other reasons involved. The engine of your vehicle may also be damaged or there might be some other issues that contribute to affecting your car’s performance which in turn become dangerous for a good environment.

6. Earsplitting Engine Sound

You will notice that rough and ear splitting noise is being produced by your car’s engine if the oxygen sensor is not working properly. We know that it is one of the common signs that are very easy to detect because such noise cannot be ignored. You must consult a mechanic and get this issue fixed as soon as possible. If you wait for so long to fix this issue, you will lose your engine and will have to install a new one.

Some people think that every engine has some noise but this is totally wrong. A well-functioning engine never produces noise and is relatively silent. When you notice that your car is producing noise when running or when idle, it means it has faulty oxygen sensors.

The noise may also be produced at the time when you apply brakes. This noise is so unpleasant that a person cannot wait for so long to get this issue fixed. It not only disturbs you but also others on the road that are near you. You will find difficulty in starting and accelerating your car due to poor fuel combustion.

7. Overheating of Engine

Your engine will start overheating due to a bad oxygen sensor. You should know that there are many side effects of overheating on the performance and body of the engine. It can get damaged badly along with damaging other parts of your car due to getting overheated. Thus, it will cost you a lot of money as you will have to change the engine as well as replace other damaged parts of your car.

Let us tell you that the overheating of an engine majorly occurs due to the problems of an electrical system but in some rare cases, the damaged or bad oxygen sensor results in overheating the engine. Plus, the sensors become worn badly so you will need to replace them.

8. Failure of Catalytic Converter

A catalytic converter is considered one of the most important parts of your vehicle. It is involved in the emissions system of your car and is similar to the oxygen sensors. The purpose of a catalytic converter is to control the amount of air in your vehicle’s exhaust system which in turn reduces the toxic gasses that are released by your vehicle into the atmosphere.

As a catalytic is a major part of your car, its functioning greatly depends upon the oxygen sensors. So, when there is an issue with the oxygen sensor, you will notice that the catalytic converter is also not working properly.

We can say that the failure of the oxygen sensor results in failing the catalytic converter in no time. Now you must be wondering how you would know that the catalytic converter is not working. Let us tell you that when you notice that compression misfiring is being caused by leaky valves, the catalytic converter has failed which in turn tells you that the oxygen sensors have been failed or damaged.

Frequently Asked Questions

1. How does an oxygen sensor damage?

The oxygen sensor can get damaged due to byproducts of combustion like oil ash, fuel additives, lead, and sulfur.

2. Can a bad oxygen sensor damage your engine?

Yes, a bad engine can greatly affect your engine’s performance, timing, air to fuel ratio, and combustion intervals which in turn results in a lot of engine problems.

3. What happens if you drive with a bad oxygen sensor?

If you drive with a bad oxygen sensor, it will result in increased pollution as well as poor fuel efficiency. If you do not fix the issue for several months, you will have to face serious engine problems and might also have to replace it which will be costly.

4. What does a bad O2 sensor look like?

Bad oxygen shows different signs to you such as a bright orange or red light on your dashboard turning on that shows there is an issue with your oxygen sensor.


Oxygen sensors play a vital role in every vehicle that detects the presence of harmful oxygen. This emitted gas can be dangerous for your health as well as your vehicle. You should know that the oxygen sensors do not last for a very long time as they get damaged easily.

So, you should get them checked by a professional regularly. There are different signs that show the failure of an oxygen sensor. All these signs have been mentioned in this guide.

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