7 Bad Catalytic Converter Symptoms And Replacement Cost

bad catalytic converter symptoms

Back in the day, I bought a JDM car. Upon driving a few miles, I realized that the car was not picking up. Even if I fully pressed the gas pedal, it was not accelerating.

I shared this with my brother, who suggested that I should get the catalytic converter of my car serviced. This little piece of advice worked like a miracle for me.

The mechanic told me that the catalytic converter of my car was clogged. That was the main reason behind the poor performance of my vehicle. Since the exhaust flow was not smooth, so the working of the exhaust system was compromised. Due to this, the engine was kind of choked.

As soon as the problem of the clogged catalytic converter was solved, the complete outlook of my car was changed.

Following are the major symptoms of a bad catalytic converter:

  1. Check Engine Light
  2. Increased Emissions
  3. Strange Smell From Exhaust
  4. Reduced Engine Performance
  5. Poor Fuel Efficiency
  6. Rattling Noises
  7. Holes in the Catalytic Converter

I hope this article is of help in regards to what is a catalytic converter? What is its role in the exhaust system, and what causes its failure.

What is a Catalytic Converter?

A catalytic converter is a device that consists of a ceramic honeycomb matrix containing a catalytic coating. This coating is typically made from platinum, rhodium, palladium, or other precious metals.

A catalytic converter is designed to reduce the toxicity of emissions from internal combustion engines, such as those found in automobiles and boats.

Catalytic converters make it possible for modern society to run on unleaded fuels such as gasoline and diesel by converting the harmful pollutants found in engine exhaust into less harmful substances.

How Does A Catalytic Converter Work?

plugged catalytic converter

A car’s exhaust system contains poisonous gases such as carbon monoxide, nitrogen oxide, and unburnt hydrocarbons. These products are produced due to the engine cycle taking place in the combustion chamber.

The job of a catalytic converter is to reduce toxicity in vehicle exhaust. In the catalytic converter, a chemical reaction between air and fuel helps minimize toxicity by converting harmful pollutants into less harmful substances.

The working of a catalytic converter is such that the liquid fuel passes over the coated substrate. Chemical reactions in the presence of heat release various gases at different temperatures. The exhaust gas exits through the exhaust duct, carrying away noxious engine fumes.

What Causes a Catalytic Converter To Go Bad?

There can be several causes for a catalytic converter to go bad. Some of the major reasons are listed below:

Catalytic converter plugged up with carbon

Catalytic converter plugged up with carbon, which is a normal buildup due to incomplete combustion. It may result in a clogged catalytic converter.

Incorrect assembly of the converter

Incorrect assembly of the converter during manufacturing, for example, omission of the gasket between the pipe and converter shell or faulty O-ring sealing. These can all cause exhaust leaks resulting in reduced performance.

Catalytic converter overheating

Catalytic converter overheating can be caused by a number of factors, including engine malfunction or poor heat conduction from the exhaust manifold.

Incorrect installation

Incorrect installation of the catalytic converter is a common cause and may result in a non-working system. It is due to holes being drilled incorrectly during installation.

Overloading the vehicle

Overloading the vehicle by carrying a heavy load or being towing a trailer can give you a clogged catalytic converter. Damage, such as from a collision with a curb while parking is also a potential cause of a bad catalytic converter.

Using the wrong grade of gasoline

This clogs up the converter’s platinum and palladium catalyst because these metals do not mix well with lead found in regular gasoline. Hence, you end up with a clogged catalytic converter.

Using leaded gasoline

Using leaded gasoline in a vehicle designed for unleaded will destroy the catalyst because of the violent chemical reaction caused by its interaction with the tetraethyl lead before reaching operating temperature.

A faulty oxygen sensor

A faulty oxygen sensor can often be misdiagnosed as a failing catalytic converter, giving inaccurate readings. An oxygen sensor might falsely report.

Bad Catalytic Converter Symptoms

The catalytic converter is designed to reduce the toxicity of engine exhaust. But when you have a bad catalytic converter, its effects are anything but benign. A catalytic converter can fail in a number of ways.

If you notice any of these symptoms, have your car checked out by your mechanic immediately. You could have an exhaust leak that’s playing havoc with your vehicle’s performance.

1. Check Engine Light

You notice that the check engine light is on or that dashboard lights warn you about emissions components. It is an indication of a bad catalytic converter.

When there’s an emissions problem, your car’s computer will often search for the faulty component and activate warning lights on the dashboard. Have your car checked by a mechanic immediately to get to the root of the problem before more damage is done.

2. Increased Emissions

Your catalytic converter isn’t doing its job. If your car is emitting too much carbon monoxide, the catalyst in the converter might have become inactive due to high temperatures or time. A bad catalytic converter will never pass the emissions test.

Again, this requires the replacement of the catalytic converter. You can also check for this by having your mechanic test the converter before replacing it.

3. Strange Smell From Exhaust

Your car is running roughly and emitting an exhaust that smells of rotten eggs and burnt oil. This smell is the result of your engine running rich, which means it’s emitting more fuel than necessary.

This is a classic symptom of a bad catalytic converter. If your car emits this odor, drive it to your mechanic immediately before damage can be done to the catalytic converter or other engine components.

4. Reduced Engine Performance

When you have a clogged catalytic converter your car struggles to maintain its speed when you’re driving, and there is no underlying engine problem.

If you feel like the RPMs are higher than normal while driving, this could indicate a bad catalytic converter. Have your car checked by a mechanic.

5. Poor Fuel Efficiency

With a clogged catalytic converter you notice a significant decrease in gas mileage, especially on the highway. An exhaust leak could cause this before the converter. The lack of back pressure will cause your engine to run less efficiently and use more fuel.

The back pressure puts added strain on the catalytic converter. The catalytic converter has to work harder than normal to complete its function because of the increased toxins it has to process, resulting in lower mileage.

Have your car checked by a mechanic as soon as possible when you are getting lower than usual fuel mileage due to a bad catalytic converter.

6. Rattling Noises

You hear a clinking noise coming from under your hood. Have your car checked out by a mechanic if you hear this noise. A bad catalytic converter can damage other components of your vehicle, so have it seen as soon as possible.

While driving with a bad catalytic converter you hear strange sounds when accelerating. This could be the result of a busted catalytic converter.

If you hear strange, high-pitched clanging or other unusual noises coming from the engine, there might be exhaust gases leaking into the engine area due to a choked exhaust flow.

7. Holes in the Catalytic Converter

There are holes in the body of your faulty catalytic converter. This is a less common symptom of catalytic converter failure, but have your car checked by a mechanic if you have seen it.

The holes in the converter allow oxygen to pass through while blocking toxins, allowing some air into your engine while keeping it running cleanly. Your car won’t run correctly with this problem.

How To Test For a Faulty Catalytic Converter?

You can perform an emission test to be sure that you have a faulty catalytic converter. But a low-tech way to test for bad catalytic converters is by looking into your car’s exhaust pipe while someone else starts it.

This rules out other causes like an engine misfire or glowing plugs. If you see smoke coming out, it is most likely that the catalytic converter is not working.

Catalytic Converter Replacement Cost

In most cases, you’ll be able to fix a broken catalytic converter for less than the price of a new one.

This is because, in many states, it’s mandatory that the catalytic converter is fixed once it breaks instead of being replaced with a new one. The main reason is that your car can emit too much toxic gas if the catalytic converter is replaced with a new one.

If you’re wondering how much the catalytic converter costs, then I’ll save you some time and tell you that it varies depending on where you live. The price of this part is determined by the number of cylinders your car has since most vehicles with four cylinders have one catalytic converter, while most cars with six cylinders have 2.

The average cost of a catalytic converter replacement is about $1,000, which means you have to buy two for $2,000 if your car has six cylinders. But before you go ahead and replace it with a new one, I would advise you to check with your local mechanic first.

He might be able to fix it without spending too much money on the part itself. But if you decide not to do this and want to replace it with a new catalytic converter, then make sure that you use OEM parts.

Sometimes people skip the idea of replacing their converters because they think it’s too expensive to buy a replacement part for it and then pay labor costs as well. But this problem can be easily solved by looking up some installation guides online or buying a brand new one from Amazon or eBay at an affordable price.


The exhaust gases produced by an engine contain carbon dioxide and water vapor; however, small amounts of other harmful substances such as nitrogen oxide (NO) and unburnt hydrocarbons (HC) are also released into the open air from the engine.

It is the role of a catalytic converter to transform these pollutants into carbon dioxide and water vapor in order to maintain low emissions output. In fact, this device reduces many harmful substances by over 90%.

The significant signs of a clogged catalytic converter include a failed emission test, strange smell from the exhaust, reduced engine performance, poor fuel efficiency, rattling noises, and holes in the catalytic converter. If you observe any of these symptoms, then make sure to visit a car care professional at the earliest.

In many countries, the catalytic converter has become a target for criminals who want to get their hands on valuable metals that are needed in the production of smartphones and computers. In Norway alone, an average of 45 catalytic converters are stolen each day.

The catalytic converter is one of the most important inventions in the history of automobiles. Almost all modern cars have them even though they cause a number of problems. By 2015, 89% of all vehicles in the US had a catalytic converter installed.

Frequently Asked Questions

Can You Repair a bad catalytic converter?

It is common to repair catalytic converters rather than replace them. The reasons for this are numerous. The replacement of a converter can be very expensive and does not always guarantee that the vehicle will run as it did prior to the malfunctioning of the converter.

In order to properly differentiate between whether a catalytic converter needs to be replaced or repaired, it is important to understand how the converter works.

Can you drive a car without a catalytic converter?

Yes, you can drive without a catalytic converter. Your engine may still run without a catalytic converter, but it will produce more emissions and won’t run as efficiently. In addition to that, you might be liable for fines from the Environmental Protection Agency if you drive with no converter.

Why are catalytic converters getting stolen?

In the last few years, catalytic converter thefts have been on the rise. In fact, it is estimated that over 20,000 thefts took place last year alone in the United States. That’s a lot of precious metals going to waste!

So what do these thieves want with the catalytic converters anyway? Well, it turns out that the precious metals platinum, rhodium, and palladium are pretty expensive these days.

So I guess it’s easy money for them! In many cases, the value of the stolen metal exceeds even the value of the car itself. It seems like a good deal for them, at least.

Catalytic converters contain very small amounts of these precious metals, which means that the converter has to be laboriously dismantled and then melted down.

What is a stolen catalytic converter worth?

In most cases, a new catalytic converter costs between $800 and $2,000. However, if your car is equipped with a more expensive model, you will have to pay more money. Your insurance company will not reimburse you for the cost of a stolen converter since it is classified as vandalism.

What is the average lifespan of a catalytic converter?

A catalytic converter can last as long as 150,000 miles before it needs to be replaced. However, some crucial factors affect this figure. The first is the frequency of driving, the second is the severity of driving conditions, and lastly, the quality of installation.

Suppose you operate your vehicle on a daily basis. In that case, more than 150,000 miles can probably be achieved between change intervals if the converter was installed properly to OEM specifications using OEM grade materials.

That being said, there are some required maintenance or tune-up type maintenance that needs to be conducted on your vehicle from time to time.

The catalytic converter does not necessarily wear out or fail in the sense that it stops functioning completely. It does not suddenly “plug up” and cause you to lose power or fuel mileage. Rather, it becomes clogged gradually. It will give you clear signals before going bad completely.

Where is a catalytic converter located?

Catalytic converters are usually located under the vehicle, where they can easily be reached for replacement. They will either be attached to the exhaust system by a clamp or welded in place.

If your vehicle is rear-wheel drive, then there will probably be one converter behind each rear wheel. If it is a front-wheel drive, there will be one converter on each side of the vehicle, near where the exhaust pipe from each cylinder bank meets the main exhaust system.

On most modern cars/trucks, a catalytic converter is located under the passenger compartment of the front area. It is often under the car just in front of the rear axle.

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