10 Bad Catalytic Converter Symptoms

A catalytic converter is a vital component of a vehicle’s exhaust system. Its purpose is to convert harmful emissions from the engine into less harmful ones before they are released into the atmosphere. However, when a catalytic converter begins to fail, they are known to cause a range of symptoms that can be noticeable to the driver.

In this article, we’ll be discussing 10 common symptoms of a bad catalytic converter. From decreased fuel efficiency to strange smells and noises, we’ll cover everything you need to know to spot a failing catalytic converter and get it fixed before it becomes a major problem.

So, without further ado, let’s dive right in!

What Does a Catalytic Converter Do?

A catalytic converter is a device that’s found between your engine and the resonator or the muffler and plays an essential role in the car’s exhaust system. This device is found on most modern vehicles.

Its purpose is to reduce exhaust emissions and protect the environment by eliminate or converting harmful pollutants in engine exhaust into less harmful ones before they’re released into the atmosphere.

Catalytic converters are usually made from platinum and palladium, which act as catalysts to help with the chemical reactions inside the converter.

However, over time these metals can become clogged with soot or debris, causing the converter to become less effective at cleaning up exhaust fumes. When this happens, you may notice some bad catalytic converter symptoms.

Potential Issues With a Catalytic Converter

In general, catalytic converters last for 10 years or around 80,000 miles. And although it is one of the long-lasting parts of your car’s exhaust system, that number can vary depending on a variety of factors, such as the type of car and the driving habits of the person behind the wheel.

but like any other part of your vehicle, it will eventually get worn out and need to be replaced.

Some car models even have a service schedule for maintaining or replacing them, but most people choose to not follow this due to the expensive replacement cost.

Like any other part of your vehicle, the catalytic converter is not perfect. There are a few potential issues that can arise with “cats” as they are called, which is why it is good to be aware of the symptoms of a bad catalytic converter.

And a it is actually the third most common car repair, related to the check engine light.

The reason for that is they they are know for clogging up and taking damage as they are located under the car. This will inevitably result in reducing their effectiveness and could cause your engine to take damage.

Another issue is that the converter can get often take damaged from exposure to oil or coolant leaks due to a faulty cylinder head gasket, which eventually will cause the catalytic converter to clog.

This will result in restriction of the exhaust airflow and likely decrease engine performance and put unnecessary stress on your engine. So if you experience issues starting your car, sluggish engine performance, or even quits after a while, a clogged converter could be the blame. Lets take a look at the most common symptoms in mor detail.

What are the Symptoms of a Bad Catalytic Converter?

1. Check Engine Light

A check engine light could mean many things. If the check engine light comes on, you’ll want to have it checked with a compatible OBD scanner.

That means you’ll have to take it to a mechanic or an auto parts store that can check the error code for you. If it comes back as P0420 or P0430, it is likely your catalytic converter is bad or that the oxygen sensor needs a replacement.

Related: Cost to Replace Muffler and Exhaust Pipe (And Benefits)

2. Reduced Acceleration

If you notice your car has reduced acceleration or losing power, the chances are high that you are driving with a bad catalytic converter.

Reduced acceleration is one of the common catalytic converter symptoms, if you noticed your car taking longer to accelerate, especially when going up a hill, it is most likely clogged.

You should immediately diagnose the problem to see what is causing the reduced acceleration.

3. Sluggish Engine Performance

Another bad catalytic converter symptom is sluggish engine performance. If you noticed your engine is not running as smoothly as it used to, then it could be because your catalytic converter is not working properly.

A clogged catalytic converter can create significant backpressure, which means your engine will “choke” on the buildup of exhaust gas which results in a loss of acceleration and power, causing jerky movements.

If the exhaust flow is severely restricted, your car might completely stall.

4. Increased Fuel Consumption

Does it feel like you constantly filling up the tank lately? If you got a clogged catalytic converter, your engine has to work much harder to compensate for the loss of power. This means you’ll like to have increased fuel consumption.

5. The Smell of Rotten Eggs or Sulfur From the Exhaust

The smell of rotten eggs or sulfur from the exhaust is a sign of a clogged catalytic converter. The restricted exhaust flow will make the engine run rich, which means too much fuel.

The culprit for the odor is usually an abundance of unburnt fuel, which are harmful to both humans and the environment.

6. Rattling or Other Noises

If you hear a rattling noise from your exhaust system when you rev your engine or start your car, it could be because of a bad catalytic converter.

The rattling noise is usually caused by the catalyst-coated “honeycomb” inside the converter. The honeycombs can begin to collapse and break apart, which will cause small pieces to rattle around inside.

As the honeycomb breaks down, the rattling will get worse over time. It is a good idea to ask a friend to press the accelerator pedal while you try to listen to where the noises are coming from.

7. Starting Issues

If your car starts for a few seconds and then dies, or if you have an issue starting your car, it could likely be because of a clogged catalytic converter.

The restriction in your exhaust system will give the engine a hard time getting rid of the exhaust fumes, creating backpressure that will choke the engine.

Your car might start for a few seconds because it may take 2-3 seconds for the pressure to rise enough to choke the engine, eventually killing it.

8. Engine Misfires

Can a clogged catalytic converter cause a misfire? The answer is YES! A clogged or failing catalytic converter can cause the engine to run rich, which means there is not enough oxygen being mixed with fuel for proper combustion.

This can cause the converter to overheat and can have damaging impacts on your car’s engine. If your engine is misfiring, it’s important to get it fixed as soon as possible to avoid further expensive repairs.

9. Increased Emissions

Today, most countries and more than 30 US states require some level of emissions testing by law. If your car fails an emission test, the chances are high that you have a bad catalytic converter.

It would be best if you let a professional mechanic take a look to determine what the problem is. If it is your catalytic converter, you will likely continue to fail the emission test until it is fixed or replaced.

10. Excessive Heat Under the Vehicle

If you notice discolored housing or excessive heat coming from under your car, it could be because of a clogged catalytic converter. The converter can get extremely hot and even cause a fire.

It could also create excessive heat inside the engine, causing it to overheat, which could result in expensive repairs. Therefore you shouldn’t drive your car if you notice this symptom.

What You Can do About a Clogged Catalytic Converter

First, you need to be sure that the catalytic converter is not broken or clogged beyond repair. If it is, then the only solution is to replace it. Installing a new one usually takes an hour.

If your catalytic converter is only partially clogged, there are a few things you can do to try and clean it out.

You could use a catalytic converter cleaner, which you can find at most auto parts stores. Or, you could remove the converter and physically clean it with warm water and degreaser, then use a pressure washer at low pressure.

If you go the DIY route, be sure to consult your car’s owner’s manual or a professional mechanic before you do anything.

Catalytic Converter Theft

In recent years, catalytic converter theft has become a massive problem in some areas where the catalytic converters are easy to access and quickly removed with a battery-powered saw.

The reason is the three main elements in a catalytic converter: platinum, palladium, and rhodium. The value of these metals has been on the rise in recent years, and with that, so has catalytic converter theft.

The theft usually only takes a minute or two, and the thief can then sell the catalytic converter for scrap.

While the average cost of a new catalytic converter ranges from $800 to $1200, depending on the make and model of your vehicle, the catalytic converter scrap price is between $300 to $1500.

The best way to protect your catalytic converter is to park in a well-lit and visible area, and if you have a garage, park your car inside it. You can also buy a catalytic converter anti-theft device that makes it more difficult for thieves to remove it.

If you wish to learn more, here is a guide about how to protect your catalytic converter from getting stolen by Adam at Mechanicbase.com


Can You Drive With a Bad Catalytic Converter?

It is highly recommended not to drive with a faulty catalytic converter. You might be able to drive for a certain distance, but eventually, the engine will start to misfire and run poorly. And in some cases, it can also cause damage to other parts of the car’s engine, leaving you with more expensive repairs.

How Long Does a Catalytic Converter Last?

The lifespan of a catalytic converter is about 10 years, or anywhere from 40,000 to 100,000 miles. However, many factors can shorten its lifespans, such as engine misfires, oil leaks, and driving habits.

What Is the Cost Of replacing a Catalytic Converter?

The cost of replacing a catalytic converter can range from $800 to $1200 or more, depending on the make and model of your vehicle.

Can You Drive a Car Without a Catalytic Converter?

Driving without a catalytic converter will not harm your car, but it is illegal in many countries and states. If you are thinking of removing your catalytic converter, or if it got stolen, you shouldn’t drive your car. The catalytic converter helps to reduce pollution, and without it, your vehicle will not fulfill the emission standards.

What Does a Bad Catalytic Converter Sound Like?

If your car’s catalytic converter is bad, you might hear a rattling noise. Especially when first starting your car or when you rev the engine.

Can You Clean a Catalytic Converter?

Yes, if the catalytic converter is clogged, you could try cleaning it. Make sure to use a cleaner specifically designed for it. The reason is that the catalyst inside the converter helps to reduce pollution, and cleaning it wrong can actually make it less effective.


Now you know what potential issues there is with catalytic converters and the symptoms to determine if yours might be causing problems.

If you experience any of the listed symptoms above, you should not keep driving before diagnosing what is causing the problem.

A catalytic converter might be expensive to replace, but driving with a bad catalytic converter may result in even bigger repair bills.

I hope you found this article helpful, and stay safe on the roads!

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Rickard Cefalk

Rickard is the owner of Caraspect.com and a dedicated and avid do-it-yourselfer who has always enjoyed working on his own vehicles since childhood. He now devotes his time to sharing his expert knowledge of car maintenance and other car-related information through his website.

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