7 Warning Signs of Catalytic Converter Failure Symptoms: How to Spot Them

Nov 9


Jane Scaplen

Jane Scaplen

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A catalytic converter is a crucial component of a vehicle’s exhaust system, responsible for reducing harmful emissions. However, when it fails, it can lead to a variety of issues, including decreased engine performance and even damage to the vehicle. Understanding the warning signs of catalytic converter failure symptoms is essential for maintaining optimal vehicle performance and preventing further complications.


In this blog post,7 Warning Signs of Catalytic Converter Failure Symptoms: How to Spot Them Articles we’ll discuss the role of catalytic converters, how to identify common catalytic converter failure symptoms, additional warning signs, and steps to diagnose, repair, or replace a failing catalytic converter, as well as preventative measures to extend its lifespan.

Key Takeaways

  • Catalytic converters play an important role in reducing harmful emissions from vehicles, yet can be susceptible to issues that affect performance and emission.
  • Poor acceleration, reduced engine performance, illuminated check engine light and unusual smells from exhaust are warning signs of catalytic converter failure.
  • Regular maintenance & use of fuel additives are effective preventative measures to extend the lifespan of a catalytic converter.

Understanding the Role of Catalytic Converters

Catalytic converters are integral in mitigating harmful emissions from a vehicle’s engine. These components are designed to convert toxic gases, such as carbon monoxide and sulfur dioxide, into less hazardous substances like carbon dioxide and water. This action aids in curbing pollution while preserving the vehicle’s overall performance.

However, catalytic converter problems, including clogged catalytic converters, can arise, causing a myriad of issues that can affect a vehicle’s performance and emissions.

How Catalytic Converters Work

Catalytic converters operate through a series of chemical reactions that transform harmful gases into less toxic substances. Inside the converter, a honeycomb structure coated with precious metals like platinum, palladium, and rhodium serves as a catalyst for these reactions. As exhaust gases pass through the honeycomb channels, the catalyst enables reduction and oxidation reactions, converting nitrogen oxides, carbon monoxide, and hydrocarbons into nitrogen gas, oxygen gas, carbon dioxide, and water.

Bear in mind that a clogged converter can instigate trouble, resulting in diminished engine performance and other complications.

Legal Requirements for Catalytic Converters

Catalytic converters are legally required in most vehicles to help reduce emissions and meet environmental standards. In the United States, requirements vary by state, but federal law prohibits the removal or replacement of a properly functioning original equipment (O.E.) converter. Failing to replace a clogged catalytic converter can result in additional engine damage, violation of federal regulations, and a failed emissions test.

You must make sure your vehicle’s catalytic converter is working optimally to avert potential repercussions caused by a bad catalytic converter.

Identifying Catalytic Converter Failure Symptoms

Recognizing the symptoms of catalytic converter failure is key to tackling potential problems before they worsen. Some common symptoms include:

  • Poor acceleration
  • Reduced engine performance
  • An illuminated check engine light
  • Unusual smells from the exhaust

Identifying these warning signs aids in diagnosing and resolving any catalytic converter issues, allowing your vehicle to continue operating at its best and reducing harmful emissions.

Poor Acceleration and Reduced Engine Performance

One of the most noticeable symptoms of a clogged catalytic converter is poor acceleration and reduced engine performance. A clogged converter restricts the flow of exhaust gases, which can lead to decreased power and difficulty maintaining speed. Additionally, neglecting this issue can result in further damage to the engine and other components.

Promptly addressing any abnormal rattles or changes in acceleration is vital to prevent added complications.

Illuminated Check Engine Light

Another common indicator of catalytic converter failure is an illuminated check engine light. The car’s internal computer is designed to detect changes in exhaust gas levels and will activate the check engine light when an issue is detected. If your check engine light is on, it’s important to seek a professional diagnosis to ascertain the cause, as it might be due to a failing catalytic converter or other possible issues.

Unusual Smells from Exhaust

A failing catalytic converter may also produce unusual smells from the exhaust, such as a rotten egg or sulfur odor. This smell is caused by the presence of hydrogen sulfide, a sulfur derivative that is supposed to be converted into odorless substances by the catalytic converter. If the converter is not functioning correctly, hydrogen sulfide is released, resulting in the pungent odor.

Timely identification and resolution of this issue can help prevent further damage to the catalytic converter and other components.

Additional Warning Signs of Catalytic Converter Issues

Beyond the usual bad catalytic converter symptoms mentioned earlier, there are other warning signs that may point to catalytic converter issues. These can include rattling noises under the vehicle, overheating of the catalytic converter, and a failed emissions test.

Being aware of these additional warning signs can help you diagnose and address any potential catalytic converter problems before they lead to more severe consequences.

Rattling Noises Under the Vehicle

Rattling noises under the vehicle can be a sign of a damaged or failing catalytic converter. These noises can be caused by a loose heat shield or internal damage to the converter itself, such as a collapsing honeycomb structure.

If rattling noises emerge from underneath your vehicle while it’s running or when the engine is revved, immediate action is needed to prevent further damage to the catalytic converter and other components.

Overheating of the Catalytic Converter

Overheating of the catalytic converter can lead to further damage and engine issues. Potential causes for an overheating catalytic converter include leaking fuel injectors and an excessive amount of hydrocarbon (HC) in the exhaust stream. If the converter overheats, it can cause damage to the internal components, such as the catalyst substrate, due to melting or warping.

This can lead to poor fuel efficiency, a decrease in effectiveness in reducing emissions, as well as potential engine overheating and engine misfires, including engine misfire.

Failed Emissions Test

A failed emissions test can be a potential indicator of a faulty catalytic converter. The catalytic converter is responsible for reducing the amount of harmful emissions from exhaust gases; when it is not functioning correctly, it is unable to convert these emissions as effectively, resulting in higher levels of pollutants being released into the atmosphere. Thus, the vehicle will not meet the required emissions standards and will not pass the test.

Ensuring your vehicle’s catalytic converter is functioning properly is important to avoid failing an emissions test and to reduce environmental impact.

Diagnosing and Confirming Catalytic Converter Failure

Once you’ve identified the potential symptoms and warning signs of catalytic converter failure, it’s important to properly diagnose and confirm the issue. Several diagnostic methods can be employed to verify a clogged or malfunctioning catalytic converter, such as inspecting the exhaust backpressure, utilizing a vacuum gauge, and conducting an emissions test.

An accurate diagnosis allows you to take appropriate steps to repair or replace the failing catalytic converter and restore optimal vehicle performance.

Repairing or Replacing a Failing Catalytic Converter

If you’ve diagnosed and confirmed a failing catalytic converter, the next step is to repair or replace it. There are several options available, including:

  • OEM (Original Equipment Manufacturer) replacement catalytic converters
  • Aftermarket catalytic converters
  • High-flow catalytic converters
  • Catalytic converter delete pipes

Aftermarket exhaust system upgrades can also help improve the performance of your engine and catalytic converter.

Replacement of a catalytic converter requires adherence to a specific procedure. This includes:

  1. Elevating the vehicle
  2. Locating the catalytic converter
  3. Clearing any obstructions
  4. Applying penetrating oil
  5. Unmounting the oxygen sensor
  6. Loosening the bolts
  7. Removing the old catalytic converter
  8. Fitting the new catalytic converter
  9. Fastening it with bolts
  10. Reattaching the oxygen sensor
  11. Lowering the vehicle
  12. Testing the new catalytic converter.

Preventative Measures to Extend Catalytic Converter Lifespan

Embracing preventive measures can prolong the lifespan of your catalytic converter and keep your vehicle running at peak performance. Adhering to the manufacturer’s recommended service schedule, including replacing the air filter, oil changes, and coolant checks, can ensure the catalytic converter functions optimally. Additionally, the use of fuel additives can help optimize engine efficiency, reducing the number of carbon particles entering the exhaust and minimizing the strain on the catalytic converter.


In conclusion, understanding the role of catalytic converters, recognizing common failure symptoms, and being aware of additional warning signs are essential for maintaining optimal vehicle performance and preventing further complications. By properly diagnosing and confirming catalytic converter failure, you can repair or replace the faulty component and restore your vehicle’s performance. Furthermore, implementing preventative measures, such as adhering to the manufacturer’s recommended service schedule and using fuel additives, can help extend the lifespan of your catalytic converter and minimize the likelihood of future issues.

Frequently Asked Questions

What happens when your catalytic converter starts going out?

Driving with a bad catalytic converter will cause sluggish engine performance, reduced acceleration, a smell of rotten eggs or sulfur from the exhaust, dark exhaust smoke, extreme heat coming from under the vehicle, and difficulties operating at slower speeds. These symptoms should be addressed as soon as possible for the continued functioning of your vehicle.

What are the 3 most leading failures of a catalytic converter?

The three most common causes of catalytic converter failure are overheating, melting and breakage.

How can I diagnose a clogged catalytic converter?

To diagnose a clogged catalytic converter, inspect the exhaust backpressure, utilize a vacuum gauge, and conduct an emissions test.

Can fuel additives help extend the lifespan of a catalytic converter?

Yes, fuel additives can help extend the lifespan of a catalytic converter by optimizing engine efficiency and minimizing the strain it is exposed to.

What preventative measures can I take to maintain optimal vehicle performance and extend the lifespan of my catalytic converter?

To maintain optimal vehicle performance and extend the lifespan of your catalytic converter, adhere to the manufacturer's recommended service schedule, replace the air filter regularly, perform regular oil changes and coolant checks, and use fuel additives.