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Can an Aftermarket Exhaust Cause a Check Engine Light?

Can Aftermarket Exhaust Cause Check Engine Light

Getting an aftermarket exhaust system is one of the best ways to increase the sound and performance of an engine.

The first third generation Chevy Camaro I bought had issues with the exhaust system that caused it to make horrible noises during acceleration. This is the car that got me acquainted with how an exhaust system works.

There’s no way to guarantee that any aftermarket exhaust part won’t throw an engine code – an aftermarket exhaust can cause a check engine light.

In what follows we’ll be looking at the different component of an exhaust system, as well as how they work together as we explore the parts of an aftermarket exhaust that can cause a check engine light.

There’s a Difference Between an Aftermarket Exhaust and an Aftermarket Muffler

Simply put: an exhaust helps your engine expel gases produced after combustion, and a muffler is designed to reduce the sound those gases make as they travel through the exhaust system.


An exhaust system consists of pipes and components that guide exhaust gases from the engine into the atmosphere.

Along the way exhaust gases travel through components like a catalytic converter.

Its job is to break down toxic gases into less harmful compounds before being released into the air.


One of the final components of the exhaust system those gases will travel through is the muffler.

Its job is to suppress the amount of sound the engine and gases make as they travel through the exhaust system.

This is accomplished through a series of chambers, partitions and tubes designed to absorb the noise and reduce high pitched frequencies.

The Parts That Make Up a Stock Exhaust System Are the Same Parts That Make Up an Aftermarket Exhaust System.

The Parts That Make Up a Stock Exhaust System Are the Same Parts That Make Up an Aftermarket Exhaust System.

The duty of a vehicle’s exhaust system is to carry away harmful gases created after the combustion process.

It also works to keep potentially dangerous chemicals like carbon monoxide, nitrogen oxide and hydrocarbons away from the interior of your automobile.

Warning: Here comes an oversimplification: An exhaust system consists of a series of components and piping.

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Below are the basic components of an exhaust system:


The exhaust system begins with the exhaust manifold. Made of cast-iron, it bolts directly onto an engine block.

This allows exhaust gases to travel from the combustion chamber into the exhaust system to the catalytic converter.

Catalytic Converter

We’ve talked a bit about the catalytic converter and its important role of cleaning the toxic exhaust gases and turning them into less harmful emissions.

This component works to reduce air pollution by converting those unburned chemicals mentioned above through a catalyst that turns them into carbon dioxide and water before coming out of the tail pipe.


We’ve also talked a bit about the function of a muffler and how it uses a series of chambers and channels to absorb noise.

Without a muffler all vehicles with an internal combustion engine would sound MUCH louder.

Exhaust Pipe

At the end of the exhaust system is the exhaust pipe. This is where the carbon dioxide and water are allowed to escape into the environment.

Now that we have a better understanding of the individual components making up an exhaust system and the interrelated way in which they work.

Let’s now turn our attention to how an aftermarket exhaust can cause a check engine light:

ECU Incompatibility Issues

An electronic control unit is what regulates different functions in your car – it’s an automobile’s computer. A modern vehicle is home to many ECUs.

The one controlling the engine is responsible for the check engine light on your dashboard. The ECU receives messages from many sensors throughout the engine of a vehicle.

The sensor for the exhaust is called the O2 sensor (which we’ll get into later).

Aftermarket Catalytic Converter

Aftermarket Catalytic Converter

If your exhaust installation includes a new catalytic converter, this could be the component triggering the check engine light. There’s a lot of research and development that goes into building an automobile to ensure that everything works as it should.

Replacing a stock catalytic converter with an aftermarket cat can make it challenging for the ECU to understand what it’s smelling which can then throw P0420 and P0430 codes resulting in a check engine light.

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Not only that but deviating from factory hardware makes it harder for the ECU to perform its internal self-tests. Which means if your ride is subject to state emissions inspections, it’ll be harder to pass.

Regrettably, this is a risk you take when you decide to go with aftermarket parts.

Incorrect Installation

When installing any aftermarket part onto your car, fitment is crucial. Exhaust mods can improve performance and the way your ride sounds.

Some exhausts are directional which means that if it’s installed incorrectly, it can trigger a check engine light. Not only that, but you’ll notice that the exhaust note is either louder or quieter than it should be if its incorrectly installed when you crank up the motor.

An improperly installed exhaust can also cause exhaust leaks which can trigger a check engine light. Other than a check engine light an improperly installed exhaust shouldn’t cause any issues to your exhaust system or engine.

When ordering this part double check to ensure it’s the one you need for your specific application.

A Leak in the Exhaust System

Not only will an exhaust leak trigger a check engine light. But it can also hamper fuel economy.

This causes your engine to work harder which is a drain on resources. This was one of the issues I had with my Camaro. And I can tell you from experience that an exhaust leak won’t always cause a check engine light.

As such, below are some other important ways you can tell if you have an exhaust leak if there’s no check engine light:

  • increased engine noise,
  • loss of acceleration,
  • and the smell of gasoline.

My car experienced all these issues even though the check engine light didn’t come on. A hole, break or crack in any of the exhaust components can cause the check engine light to come on.

A Lack of Maintenance Could Be Another Issue Triggering a Check Engine Light

A sudden check engine light has the unsettling ability to strike fear even in those that know quite a bit about cars. The light means that something is wrong.

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Although the installation of an aftermarket exhaust part can cause a check engine light. It’s very possible that the check engine light has nothing to do with the exhaust system at all.

A check engine light could be the result of something minor like a loose gas cap, or something more major (read: costly).

When was the last time your car was serviced?

Symptoms of other issues that can trigger a check engine light include:

Misfiring which is the result of spark plugs that aren’t firing at the correct time. The result is a poorly running engine followed by fuel consumption.

A faulty MAF Sensor can be felt when your car stalls or there’s a general lack of power or poor acceleration. The mass air flow sensor calculates how much fuel needs to be mixed with the amount of oxygen coming into the engine for combustion.

Failing Catalytic Converters are no joke given the important role they play. Sometimes they just get old and need to be replaced. Be warned: this is an expensive part. Not to mention one of the most expensive parts in an exhaust system.

An Oxygen Sensor’s Role (The O2 Sensor)

Finally, we’ve been talking around this crucial component of the exhaust system with a few hints about what it does and what makes it so important.

The O2 sensor is how the exhaust system can communicate with the ECU. It’s also responsible for measuring how much unburned oxygen is in the exhaust and helps the ECU figure out what the fuel-to-air ratio should be to keep your vehicle running smoothly.

If it malfunctions, it can trigger a check engine light. This also happened on a Nissan Maxima I once owned.