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How To Test O2 Sensor With A Scanner

What Is An O2 Sensor?

An oxygen sensor or O2 sensor will be in the exhaust manifold of your vehicle.
A new Oxygen sensor

An oxygen sensor or O2 sensor will be in the exhaust manifold of your vehicle. Its main job is checking to see how much oxygen goes unburned. Meanwhile, the rest of it leaves via the exhaust system. The sensor itself will also keep the fuel mixture of your vehicle in check.

In other words, the sensor is making sure whether or not the fuel mixture is either burning less oxygen or more. In translation, the exhaust is either burning lean or rich oxygen. However, there are all kinds of factors that will play a role in how much oxygen your exhaust is burning.

This includes air temperature, air flow, coolant temperature, engine load, and many other possible factors. Of course, the O2 sensor won’t keep track of any of this. But there are other sensors that will.

What Is A Bad Oxygen Sensor?

When your O2 sensor appears to be going bad, your vehicle will begin to run with less efficiency.
A new vs old oxygen sensors
Credit: https://commons.wikimedia.org/

When that “check engine” light comes on, the first thing you need to know is what exactly is going on. Most vehicles will reveal a specific diagnostic code. If you’re familiar with them, you’ll know right away which one pertains to a faulty O2 sensor. Is your vehicle a model from the early 1980s and onward? If so, you’ll most definitely have an oxygen sensor in your vehicle.

When your O2 sensor appears to be going bad, your vehicle will begin to run with less efficiency. On top of that, you may also run into issues like having a hard time starting the vehicle itself or a jerking throttle.

Once you are able to positively identify and confirm that a bad O2 sensor is to blame, then you’ll know it’s time to replace it. Thankfully, this is easy to do and is better spending a ton of money on a professional installation.

What Are Bad O2 Symptoms?

We’ll be looking at a few of the common symptoms related to a bad O2 sensor. It is important that you use this list as part of your self-diagnosis. This way, you can be able to rule out one issue and further investigate your vehicle for another.

The following is a list of common symptoms to look out for:

Check Engine Light

There’s a reason why this exists. If this light comes on, your vehicle should be able to give you a set of diagnostic codes that relate to your O2 sensor. The diagnostic codes will depend on the vehicle you have and what may be exactly wrong with it. Your owner’s manual might have a list of diagnostic codes so you can be able to determine what exactly may be wrong with your vehicle.

Your Engine Sounds Rough

If your engine isn’t sounding as normal as it should, then that’s a universal sign of something gone wrong. At this point, you might want to take a closer look at your fuel mixture.

They say too much can be a bad thing. In this case, if your exhaust is burning oxygen that is too lean or rich, then that will obviously spell trouble for your engine. Even worse, your engine will also deal with all kinds of issues that you want nothing to do with.

A failing engine will ultimately lead to your vehicle being inoperable. We’re not kidding when we tell you to check your O2 sensor if something is wrong. Even if it’s something that appears to be less concerning.

Bad Gas Mileage

If the engine fails due to a bad sensor, so will your gas mileage. And that means the amount it consumes will be suspect. You may not know it until after the few times you’re at the pump.

If you’re spending more money than you should at the pump, then there’s a good chance you might have an O2 sensor issue. Sure, gas prices themselves are not an issue in this case. But if you see your gas mileage suffering, then maybe it’s time to replace your O2 sensor.

Emission Test Failure

Did you know that a bad oxygen sensor may expose you to something dangerous…maybe fatal? And no, we’re not joking. A bad sensor will mean coming in contact with carbon monoxide.

And of course, exposure to too much of it will cause serious illness or death. At the same time, you can also expose your sense of smell to some not so pleasant odors as well. If that’s the case, you’re going to need to replace your oxygen sensor.

Not only will doing so will save you all kinds of money, it just might save your life.

Why Does An O2 Sensor Fail?

At some point, an O2 sensor will go bad.
A bad symptom of oxygen sensor

At some point, an O2 sensor will go bad. If your vehicle goes beyond a hundred thousand miles, that’s when you need to pay special attention to it. However, you may deal with issues related to the sensor quite sooner than that.

One common factor that may cause your O2 sensor to go bad prior to your vehicle reaching the 100k mile mark is a buildup of sulfur, fuel additives, lead, and other elements of combustion. This buildup may lead up to some issues that may also affect your car’s electrical system.

If you’re at the pump, the smart thing to do is choose the quality of gasoline. Gasoline that’s low in quality may also hasten the early demise of a sensor.

How To Test An O2 Sensor With A Scanner

To test an O2 sensor to ensure that it's working properly, you’re going to need an OBD2 scanning tool.
An OBD2 scanner can help you to diagnose the oxygen sensor problem yourself.
Credit: https://commons.wikimedia.org

To test an O2 sensor to ensure that it’s working properly, you’re going to need an OBD2 scanning tool. The following is a list of steps that you need to follow in order to perform a proper scanning test:

Step 1

Using the diagnostic link connector (or DLC) in your vehicle, plug in the OBD2 scanner. If you need to know where your DLC is, please consult with the owner’s manual that goes with your vehicle. Your DLC should have 16 triangle-shaped pins located in its port.

If you cannot locate the DLC or the pins, consult with your owner’s manual or with online sources.

Step 2

In order for the scanner to work properly, turn the ignition on your vehicle. But leave the engine off. This way, the scanner will communicate with the onboarding system.

If you are not getting a reading from the scanner or if its blank, try reconnecting or giving it a good shake or two. Depending on the scanner you use, you’re going to need your vehicle’s ID number handy. You also might need to enter any additional information like your vehicle’s make, model, or year.

To note, not every scanner will be able to ask for this information.

Step 3

Once you’ve successfully activated the scanner, search for trouble codes or “codes”. Depending on your scanner, the labeling will be different.

Step 4

Find the system that needs troubleshooting. Once you’ve found it, you should see a code or two pop up. Either they will be in a “pending” mode or “active”.

Remember, there will be other types of codes as well. The active codes are the codes that activate your “Check Engine” light. Of course, these are the type of codes that will tell you that there is a problem with your vehicle.

A pending code will mean that you’ll have an issue that has yet to be active. For example, something will fail once. If it fails again, that’s when it will switch from “pending” to “active”.

Step 5

This is where you need to translate the code. The scanner will look at the issue and will give you a code. If you’re not familiar with the codes, be sure to consult with the scanner’s manual or research the codes online. At this point, you may need to find the code and search “oxygen sensor” along with it. This will also give you an opportunity to learn some of the codes that you might make a note of so you can easily identify them for future reference.

Note: To save you time, we’ve taken the liberty of including these codes that are common with O2 sensors. They are as follows: P0030, P0031, P0036, P0037, P0130, P0131, P0132, P0133, P0134, and P0135.

Bottom Line

An oxygen sensor is one of the most vital parts of your vehicle. Whether you know it or not, if anything happens to it, there’s a good chance that it can cause some issues if you neglect it. Know the common symptoms and always err on the side of checking on your O2 sensor to see if this may be an issue.

Alternatively, you can rely on the services of a professional mechanic to diagnose the issue for you. However, you should be able to diagnose the problem yourself using a scanner.


What does a car do when the oxygen sensor is bad?

As mentioned before, some common issues will occur in the event of a bad oxygen sensor. This will include engine irregularities, poor fuel consumption, bad emissions, among others. Your vehicle may not start properly due to poor engine efficiency.

Can you drive a car with a bad O2 sensor?

The short answer: no. It is highly recommended that you should not drive a car that has a bad O2 sensor. One of the reasons may be that you probably won’t be aware of how advanced the damage to the engine may be.

At any point, a failing engine will quit on you and will put you in a potentially dangerous situation. Also, a car that fails an emissions test can also pose a dangerous health risk. A faulty O2 sensor can lead to exposure to carbon monoxide.

Carbon monoxide is odorless, colorless, and tasteless. But nonetheless, it can kill you if you’re exposed to just enough of it.

Will a bad O2 cause sputtering?

It can. Along with some jerking. To ensure that your oxygen sensor may be the actual culprit, be sure that the “Check Engine” light is one.

It can also cause some other issues like engine hesitation as well.

Will a bad oxygen sensor cause a car to not start?

While it can cause your car to have a hard time starting, it will not directly cause the vehicle to not start at all. It is a symptom of another issue that might be affecting the ignition system or the fuel pump.

How much does it cost to fix oxygen sensors?

The price will likely depend on how you want it replaced. If you’re doing it yourself, expect the costs to keep you just below $100. This will depend on the type of oxygen sensor that you buy.

However, if you choose to rely on a professional mechanic the costs will add up. Expect the bill to be somewhere between $100 to $400.

Can a bad O2 sensor cause a gas smell?

It may. In fact, the air and fuel mixture can cause an odor that may smell like rotten eggs. That obviously is far worse than a gas smell on its own.

Can a bad O2 sensor cause a car to cut off?

Your car may be susceptible to stalling in the event of a bad O2 sensor. Other symptoms to look out for if it has yet to stall will include some hesitation or misfiring.

When should you replace O2 sensors?

Regular maintenance of your vehicle is always essential. And you’d be wise to stay on top of your vehicle in terms of performance and how often you should replace certain parts. However, an O2 sensor is one of those parts that don’t get routinely replaced after so many miles. But as a rule of thumb, you should consider getting it replaced every 100,000 miles regardless of the condition that its in.

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