What Happens If You Remove O2 Sensor?

By July 31, 2020August 23rd, 2020Common Questions

Do you have a failing O2 sensor? Or are you simply curious as to what happens if you remove the O2 sensor from a car. Can removing O2 sensors increase horsepower? Well, that’s  a lot of questions. Let’s cover them in detail! 

To keep it brief – removing O2 sensors could cause your car to have any of these symptoms: bad fuel economy, reduced performance and failed emission test. If you have installed performance parts like exhaust headers and nitrous in your car, your O2 sensor could hinder the performance gain by reducing the amount of fuel injected for combustion. This happens because your O2 sensor detects excessive pollution and is trying to reduce the pollution at a cost of performance. This is why performance enthusiasts sometimes remove O2 sensors from their cars. 

Was that too complicated? I will go simpler now I promise 🙂

How Does Your Car Use Oxygen?

To deliver power, your car engine needs to ignite fuel and create combustion. This combustion absorbs oxygen. To have more power, it requires a bigger combustion which in turn requires more Oxygen. Fuel is injected into the combustion chamber, whereas Oxygen comes from the atmospheric air that’s sucked in by the car’s air intake.

Combustion generates toxic exhaust gases that will exit the car through the exhaust system. These exhaust gases contain toxic molecules like Carbon Monoxide, Hydrocarbon and Oxygen leftover from the combustion.

What’s The Function Of O2 Sensor?

The amount of oxygen and fuel in the combustion chamber must be optimal. Too little fuel means that combustion is limited and the performance of your car is also limited. Whereas too much fuel means that not all of it can burn – resulting in unburned fuel to exit into the exhaust system causing wastage and extra pollution.

This is where the O2 (oxygen) sensor comes in. An O2 sensor is responsible to measure the amount of Oxygen left in an exhaust gas. This reading is sent to the ECU (car’s computer) for it to identify how much fuel should be injected next.

Too much oxygen leftover means that there’s not enough fuel in the combustion chamber. Whereas too little oxygen leftover means that there’s too much fuel in the combustion chamber. The ECU also uses other factors to identify how much fuel to be injected – but O2 sensor plays the major role.

There should be at least one oxygen sensor in a car – located in the exhaust system, right before the catalytic converter. Typically, there is more than one oxygen sensor in a car – especially those with a bigger engine. These additional sensors are mounted on the exhaust manifold. One oxygen sensor per cylinder.

illustration of a car exhaust system
O2 sensors could be placed here in the exhaust manifold. One O2 sensor for each cyllinder.
O2 sensor could be placed here before the Catalytic Converter.

How Does O2 Sensor Work?

An O2 sensor is mounted onto an exhaust pipe – half of the body inside the exhaust, and the other half outside. The O2 sensor reads oxygen levels on both inside the exhaust and outside. The difference in O2 will create a voltage spike – indicating how low or high the O2 level is inside the exhaust. The higher the voltage spike, the bigger the difference in O2 levels. 

Oxygen sensor mounted on exhaust
The head of O2 sensor. This part is mounted into the exhaust pipe.

High voltage reading indicates that the O2 level in the exhaust is very low – which means there’s too much fuel in the combustion chamber. Using these figures, the car’s ECU can decide how much fuel should be injected for the next cycle. Below are the typical readings from an O2 sensor.

  • 0.1V – too much Oxygen leftover, not enough fuel
  • 0.45V – optimal
  • 0.9V – Too less oxygen leftover, too much fuel
Image of Oxygen Sensor
The head of O2 sensor. This part is mounted into the exhaust pipe.

What Happens If You Remove O2 Sensor?

People usually remove the oxygen sensor if they are very serious about improving their car performance. Oftentimes, when installing performance parts like exhaust headers and nitrous, your O2 sensor will sense too much pollutant and leftover fuel from the exhaust gas. These readings could cause the ECU to inject lesser fuel and hinder performance gain. Not to mention, the O2 sensor will also cause the check engine light to turn on. 

That’s good and all for the performance. However, O2 sensors are included to provide an optimal ride for the average people – good performance, good fuel economy and low emission. With the O2 sensor removed, your ECU can no longer calculate how much fuel should be injected. The ECU will fallback to its default value and always inject the same amount of fuel every time. This could cause either low performance or horrible fuel economy.

What Are The Symptoms Of A Bad O2 Sensor?

Remember – a bad O2 sensor means that your car does not know whether it’s injecting too much fuel or too little fuel. This can cause several different things.

Check Engine Light Turned On

Your ECU will notice that an O2 sensor is not responding. This will cause the check engine light to turn on. However, this does not always mean that an O2 sensor is bad. Check engine light can be turned on for many other reasons – so bring your car to a mechanic if you don’t know why!.

Reduced Performance

A sudden reduction in performance can also indicate that an O2 sensor is bad. Without an O2 sensor, your ECU would not know that it’s lacking in fuel injection – causing your car to keep driving with a restricted fuel.

Bad Fuel Economy

This point is exactly the opposite as above. Without an O2 sensor, your ECU would not know that it’s injecting too much fuel – causing your car to keep driving with wasted fuel every time. If this is really the case, you could also tell by looking at your exhaust fumes – they might be darker in color. This is the unburned fuel exiting the car through the exhaust system.

Failed Emission Test

With a working O2 sensor and a Catalytic Converter, your exhaust gas should contain majority water vapor and carbon dioxide. Now that you have wasted fuel exiting through your exhaust, you could fail the emission test. This is especially important if your state requires you to perform emission tests regularly. 

Common Causes Of Bad O2 Sensor

Contaminant 

O2 sensors can go bad if it’s exposed to too much contaminant in the air. This happens if an air filter is too dirty or they use a performance air filter that’s too open – allowing contaminants to enter into the engine. These contaminants can cause wear and tear damages to O2 sensors or simply accumulate on the O2 sensor – causing it to be less sensitive. If you are interested to know about performance air filters – the pros and cons, then I have an article about that here.

Wear And Tear

O2 sensors are wear and tear components. They should be replaced after every 90,000 miles or so. This is because the O2 sensors are working under high heat and pressure from the exhaust gases – causing wear and tear damages to its parts. After 90,000 miles, your O2 sensor will likely not be as sensitive anymore – where you have to replace them.

How To Fix Broken O2 Sensor?

People usually remove the oxygen sensor if they are very serious about improving their car performance. Oftentimes, when installing performance parts like exhaust headers and nitrous, your O2 sensor will sense too much pollutant and leftover fuel from the exhaust gas. These readings could cause the ECU to inject lesser fuel and hinder performance gain. Not to mention, the O2 sensor will also cause the check engine light to turn on. 

That’s good and all for the performance. However, O2 sensors are included to provide an optimal ride for the average people – good performance, good fuel economy and low emission. With the O2 sensor removed, your ECU can no longer calculate how much fuel should be injected. The ECU will fallback to its default value and always inject the same amount of fuel every time. This could cause either low performance or horrible fuel economy.

Conclusion

We have discussed quite a lot. O2 sensors are an important part of the engine. It is almost always a good idea to have them installed and working correctly. Unless you want to go to the extreme and focus on your car performance. Even if you go to the extreme, removing the oxygen sensor alone will not increase performance – it will only be an impact once you start installing performance parts like headers and nitrous. 

I hope you find this a good read. Check out my other articles for more car knowledge 🙂

Ifandi S.

Ifandi S.

Passionate about everything mechanical. Ifandi has been involved with motorcycles and cars since the old days - in his family's auto parts shop. Want to keep in touch? Scream "STRAIGHT PIPEEEEE" at the top of your lungs and Ifandi will show up.

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