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Can a Bad O2 Sensor Cause Misfire? (All You Need to Know)

Car owners around the world can have a headache when dealing with different car issues. Not all of them are similar and not every one of them is easy to solve on our own. Gladly some of the issues can be easily handled with some guidance and help from the internet these days.

However, identifying the main cause of a misfire can be challenging for a person that just started his journey of owning a vehicle for the first time. Furthermore, in some cases, there are just stupidly simple solutions to car issues.

People think they need a visit to the garage for these issues. However, they can be fixed by ourselves at home with the help of a few tools. Also, if we can figure out where the main issue of an engine lies, we can easily fix such problems with ease.

Car engine misfiring is one of the more common issues that a day-to-day car owner can face. But sometimes figuring out what is causing the issue in the first place can be tricky.

This is where we come in and help you identify and assess the issue of the misfiring. To know more keep reading below.

Can a bad o2 sensor cause misfire?

In certain cases when the oxygen sensor is bad, it could run but not function properly. Also, it will sound rough when it will be idle. While impacting the engine’s timing a faulty o2 sensor will give the computing unit wrong data and that would cause it to misfire. 

It is not normal for a car to misfire randomly and be without reason. There could be several reasons as to why our car might be behaving like that. However, one of the most common cases for random or multiple misfires in a car is having a faulty o2 sensor.

This happens due to the faulty sensor sending wrong information to the vehicle’s computer and thus it does not function as intended. Therefore, when there is misinformation inside the computer of the car, it starts to function randomly and causes issues.

Bad downstream o2 sensor:

This sensor is used to detect any kind of problem that might be with the converter and it fine-tunes the fuel trim. A bad downstream o2 sensor should be the cause of misfiring.

This is because if there were to be a damaged o2 sensor, this system should be supposed to detect it. The computer of your car will report a diagnostic trouble code which is P0300 and it stands for random or multiple misfires detected.

Bad upstream o2 sensor:

If there is a swing in the A/F ratio of the car, then that is a clear indicator of a faulty upstream or control sensor. When this happens fuel efficiency is decreased as there is a faulty o2 sensor that does not perform optimally. 

If there is a fuel mixture of too rich or too lean then we will encounter such a scenario.

Why o2 sensor cause misfire? How likely are o2 sensors causing misfires?

There are times when oxygen sensors become contaminated simply just because they were exposed to the harsh elements of nature. Because of that failing sensor of o2, the computer will receive wrong information and will result in misfiring.

The sensor can also cause misfires due to many other reasons and it is quite likely for o2 sensors to fail because of these failures, many misfires occur. Let us go over some of the causes for the o2 sensor to fail and cause a misfire.

Antifreeze Residue:

Antifreeze residue resulting from faulty gaskets can foul the o2 sensor and cause it to misfire.

Silicone Residue:

Silicone residue just like the antifreeze that is also the result of faulty gaskets can also have the same effect. It can cause the o2 sensor to become foul and misfire.

Elements of Nature:

Continuous exposure to the harsh elements of nature through and within the engine can contaminate the o2 sensor. This in turn causes it to misfire.

Leaded Fuel:

The use of leaded fuel is considered to release exhaust that can foul the o2 sensor, as a result causing it to misfire.

Overly Rich Fuel:

Just like leaded fuel any kind of overly rich fuel use can release exhaust that will foul the o2 sensor and cause it to misfire.

What are the symptoms of a failed O2 sensor causing misfire?

O2 sensors are usually cheap and changing them is relatively easy. While cars not working properly can be of many causes one of the most common causes for it failing is the o2 sensor malfunctioning. 

Let us go over the symptoms of a failed o2 sensor that might be causing misfire below.

Bad Gas Mileage:

We might find ourselves spending more fuel than usual. This might be an indicator of having a bad o2 sensor. This is because engines can be less efficient when they encounter oxygen to fuel ratio unbalanced.

Where the fuel is too rich or too lean. This is a rather gradual change, as o2 sensors become less effective over time and do not become a sudden failure.

Glowing Check Engine Light:

It might be from different issues from the engine, but it can also be because of the faulty o2 sensors. The range of problems can be from a loose gas cap to a multitude of things. 

This is why we should always check asap if that light is lit.

Rough Engine Sound:

This is rather a sure-fire issue when there is a bad o2 sensor. Due to the o2 sensor being faulty the engine sound will be irregular or even sound rough when it will idle. Furthermore, we should also experience stalling or duped acceleration.

Can bad o2 sensor cause a misfire in the cylinder?

Misfires can occur in a car during it is idle or when the engine might be pulling too hard under a huge load. No engine fires every cylinder all the time. At certain times a few misfires are to be expected.

However, if the issue keeps getting out of hand, then it might be due to a rather simple problem that is usually inexpensive to fix. That is if the o2 sensors have gone bad. This is rather a common case of repeated misfires in the cylinder.

Therefore, even if it is less common for a rich fuel mixture to be in a cylinder, it still occurs if the fuel injector leaks. This is because the most common cause is a bad o2 sensor.

How do you fix a faulty oxygen sensor causing misfire?

Oxygen sensors are fairly easy to diagnose and replace. Though, you cannot repair a faulty O2 sensor. So that the sensor must be replaced because of the technology and materials in its housing.      

Locate the exhaust manifold:

First we locate the exhaust manifold. We need to make sure the engine of the car is not running as the manifold gets excessively hot. Then we need to locate the old faulty o2 sensor.


We unplug the sensor using a meter and set it to 200Ω. We test the two black wires. If there is no continuity then we can safely say that the sensor is damaged.

Check for resistance:

We get a new o2 sensor that is identical to the previous one. We test again with our meter and the same settings. If we see some resistance in it then it functions properly.

Unscrew the old sensor:

We need to get an oxygen sensor socket that will not strip the old one and help us easily install the new one. We use a ratchet on the socket and unscrew the old sensor. Use protective gear while doing this.

Snug fit:

If the new o2 sensor comes with an anti-seize then lightly apply a small amount on the thread and not the sensor itself. Lastly, we screw in the new sensor and make sure to make it have a snug fit.

What is the most common cause of a misfire?

A car that has been exposed to a lot of the elements might be causing a lot of misfires. While there might be many reasons why it could misfire in the first place, here are some of the most common causes for it to misfire.

Spark plugs:

When spark plugs are worn out, they can cause a misfire.

Distributor Cap:

A cracked distributor cap can cause a misfire.

Spark Plug Wires:

If we have bad spark plug wires it can also cause a misfire.

Final Thoughts

Cars are usually machinery of critical components that can break easily and if not taken care of on a regular basis can slowly fall apart one part at a time. One of the most common issues of car engine malfunctioning is having a bad or damaged o2 sensor that can cause misfires.