Signs Of A Bad Catalytic Converter

Signs Of A Bad Catalytic Converter – How To Recognize Them?

Imagine if your car started losing power, works very poorly, or has weak acceleration. These could be the early signs of a bad catalytic converter.

Catalytic converters are one of the most important pieces of the puzzle, and they are essential for your car to run properly. So, if they are not kept in check and are worn out, the car will start to develop some symptoms.

Some of these symptoms may be clear and visible, but some can be harder to spot. The first symptoms usually start to appear early on, mostly around 120,000 miles. This is the time when the vehicle reaches a point in its life where these catalytic converters clog up and will start to fail.

When you reach 120k miles, it’s handy to give them a check-up and be aware of their condition. This is since there is a lot that can be done to prolong their lifespan and not let them get destroyed.

In this article, we are going to cover the basics of the catalytic converter, what is its role in the combustion process, and from what metals the converter is made. Then, we are going to dive into the most common symptoms of a bad catalytic converter.


Later we are going to look at the cost when it comes to replacing a catalytic converter and whether you can perform this job by yourself. And lastly, we are going to give you some simple tips on how to prevent catalytic converter thefts. So, if you want to learn about the catalytic converter, then follow along!

What Is A Catalytic Converter?

The catalytic converter is part of the exhaust system. It is a crucial component because the catalytic converter is purifying the exhaust gasses, and does not allow the release of harmful particles into the air.

By doing this, the catalytic converters are reducing the pollution in the air by a big margin, compared to 30 or 40 years ago when there were no catalytic converters. And thanks to them, we breathe cleaner and safer air.

Catalytic converters come as standard these days, and vehicles must comply with a set of regulations. These requirements become stricter every year. So, newer and better catalytic converters need to be produced to comply with these stringent standards, and carmakers need to follow them if they want to sell cars in the global market.

The catalytic converter is made out of precious metals, and that’s why it is so expensive. The core of the catalytic converter is a ceramic monolith that has a honeycomb structure.

Inside the catalyst itself are precious metals such as Platinum, Rhodium, and Palladium. These metals are really costly, and the prices for a single catalytic converter can rise to a few thousand dollars for the more high-end and precious cars.

This is also why catalytic converters are frequently stolen from cars. The thieves are out for these precious metals so they can later sell them on the black market.

Signs Of A Bad Catalytic Converter

There are many signs of a bad catalytic converter, some of which are more pronounced. Meanwhile, others need deeper troubleshooting to see what is the real culprit behind the problem. Basically, when a catalytic converter fails you will have a problem with your combustion system in one way or another.

Signs Of A Bad Catalytic Converter

In this chapter, we are going to get through most of these signs, as well as to see how they can be detected and solved in time before the catalytic converter completely fails.

Weak Acceleration

Poor acceleration is among the early signs of a bad catalytic converter. If you stamp your foot on the throttle and nothing happens, it means that something is terribly wrong and needs to be checked.

When the catalytic converter gets clogged up, the gasses cannot escape from the exhaust. In this case, heat starts to build up in the exhaust manifold. All this heat then develops a lot of backpressure. This backpressure is what will slow the car down.

If you notice that when you apply the gas pedal, and nothing happens while the car tries to stall, you need to give it a good check. If everything is okay with the engine and the fuel and ignition systems are good, you need to investigate deeper into this issue. Only then may you find your culprit.

And if nothing else solves the problem, it’s a good idea to remove the exhaust and check the condition of the catalytic converter. By doing this, you will be perfectly sure that the culprit is indeed the catalytic converter.

Engine Starts Misfiring

When an engine starts to misfire, it can be another early sign of a bad catalytic converter. If the catalytic converter is clogged up with carbon, the emissions will have no other place to escape other than returning to the engine.

The backpressure will be enormous and the combustion process will start to fail, thus creating uneven explosions inside the cylinders. These misfires can also potentially damage other components such as the pistons and O-rings. This buildup of pressure may crack the pistons, and the engine will soon lose compression.

This can and will turn into a nightmare to repair. If you disassemble your engine, the bill will start to get a lot more expensive compared to giving the catalytic converted a good cleaning. The trade-off isn’t worth it.

In this case, you will pay twice in repair bills – once for the damage in the engine, and a second time for the removal of the catalytic converter. When your engine misfires, it needs to be checked out quickly and resolved effectively.

Check Engine Light

Your car’s check engine light is also one of the signs of a bad catalytic converter. We all hate the check engine light but it exists for a reason, and that’s to remind us when there is a problem with our car. Some problems may be simple, while others are more difficult and expensive to solve.

When there is a check engine due to a fault with the catalytic converter, the light appears because of the O2 sensor readings. The O2 sensors are measuring the exhaust gasses that exit the exhaust, and it tells the computer how much air and fuel needs to be mixed inside the cylinder to provide efficient combustion.

When the catalytic converter fails, the O2 sensor gets bad readings. For example, if the converter is clogged, it will provide wrong data to the computer that doesn’t need a lot of fuel and air in the combustion chamber, and this may cause the engine to stall. If the catalytic converter is broken and nothing regulates the exhaust gasses that come out from the back, the O2 sensor may tell the car to put more fuel in, and thus increase your fuel consumption by a wide margin.

That’s why catalytic converters are important and need to always be in good condition. To solve this problem, you will have to scan your car with an OBD2 scanner. This tool will tell you what the issue is, and how to solve it. If it’s a bad O2 sensor, you will have to replace it. If it’s the catalytic converter you will have to give it a good clean.

Using a diagnosing tool is a must to diagnose this issue with the check engine light.

Difficulty To Start

Another symptom can be difficulties in starting the engine. This symptom is the most frequent in extreme cases of catalytic converter failure.

Although it can be easily confused with an ignition problem when the car has difficulty starting, as there are likely some ignition issues on the car.

If the ignition itself is perfectly fine, then it’s a good idea to give the catalytic converter an inspection. In order to perform this check-up, removal of the exhaust pipe will be necessary. You will have to unbolt the bolts that are holding the exhaust pipe in place. Then, you need to take a flashlight and peer inside the catalytic converter.

If the innards are all black and you can barely see the honeycomb structure, it means that it’s completely clogged up and needs a thorough cleaning to return it back to decent, working condition.

It is a good idea to clean the converter before it gets any worse and the honeycomb starts to dissolve in pieces from all the backpressure that it’s exposed to.

Failure To Pass Emissions

If your catalytic converter is bad, the most likely situation is that you will fail your emissions test. To register your vehicle to drive on the road, you have to pass this test.

The technician that will perform the test knows what the right emission figures are for your car. If the result of your test is above or below these values, you are going to fail. Should the results be lower than what they should’ve been, it could mean that your catalytic converter is clogged. If they are extremely high, it means that your catalytic converter is only an empty shell. Basically, there is little or nothing left from the honeycomb structure on the inside. In this case, a new catalytic converter is the only solution.

Emission tests are a good way to understand the health of your catalytic converter. There, you will have a clear understanding of what condition is the catalytic converter is in, and what are the next steps you need to take to have it serviced. If the converter is okay, you will be able to register your car. If it’s not good, you will not be able to register the car, and you will have to find a proper solution for this problem.

Rotten Egg Smell

The rotten egg scent is a dead giveaway when there is something wrong with your catalytic converter. Let’s say you give your car a smell test, and you smell a deep and disgusting odor that smells like rotten eggs. This tells us that something is wrong and needs to be looked into.

In most fuels, there is a little bit of sulfur. The role of the catalytic converter is to convert this sulfur into something that is less smelly. If the exhaust smells like sulfur, it means that the catalytic converter is not doing its job as it’s supposed to.

When you’re able to smell something like this, it’s most probable that your catalytic converter is too far gone and needs a replacement. If there is nothing left from the honeycomb structure, the only solution will be to replace it with a new one.

And remember that catalytic converters can be extremely pricey. That’s something that we are going to discuss later in this article.

Clouds Of Black Smoke

Another in the line of signs of a bad catalytic converter is the cloud of smoke at the back of your car or truck. This symptom is most pronounced if you have a diesel car or truck.

Diesel creates a lot of NOx (nitrogen oxide) particles that create this black plume smoke, and they are very toxic. When the catalytic converter is failing the NOx particles will emit out of the exhaust and cause this thick black smoke to appear. This is most obvious when the driver puts their foot on the throttle.

When this happens on the road, you can instantly notice a cloud of smoke on the back of someone’s car. This is a clear giveaway that something is wrong.

But this symptom can be easily confused with an engine that has some loose piston rings and is burning a lot of oil. Oil-burning engines can also cause black smoke to appear from the exhaust.

The positive side of this symptom is that it can be one of two things; either the catalytic converter is broken, or the engine is burning oil.

If you want to further investigate this, you can check your oil level. If the amount of oil is sufficient, it means that the catalytic converter is broken. Alternatively, the oil level drops below its recommended amount, and you needed to top up your motor oil far too often. This means that you have an issue with your engine. It’s likely that some parts are worn out and can’t seal properly.

Exhaust Leaks

Exhaust leaks may also appear if the catalytic converter is broken. These leaks happen when the backpressure is too high, and the temperatures in the catalytic converter start to rise. If the car is driven like this with many heat cycles at extreme temperatures, some holes may start to appear on the catalytic converter.

These holes are also known as exhaust leaks. When an exhaust starts to leak you are likely going to hear a hissing noise, or a sound similar to taping coming from the undercarriage.

This can be resolved by cleaning the catalytic converter, and welding then and patching up the converter housing. It’s labor-intensive work, but in my opinion, it’s worth it.

Rattling Sound

Another odd noise that can also appear when the catalytic converter is broken is a rattling sound. This happens when the honeycomb structure on the inside starts to crack and fall apart.

The rattling comes from all of the loose pieces that are juggling inside. When you apply the throttle, the pressure starts to move them about inside the housing. This movement can cause some unpleasant pops and rattles.

When you have a rattling catalytic converter, the only solution is to get a new catalytic converter. The new converter will have a good internal structure and will do its job properly, unlike the previous one.

Cost To Replace Catalytic Converter?

We discussed most of the signs of a bad catalytic converter. So, now let’s discuss what the cost is for replacing a catalytic converter. At the end of the day, we don’t want to lose any more money that’s absolutely required to get our car running again.

Catalytic converters are quite expensive, a new catalytic converter can cost anywhere from $1,300 up to $1,600. And this is only for the parts, while the labor cost is also going to cost you a couple of hundred dollars. This will depend on how much work needs to be done, and how much the local workshop is asking for. Some shops are pricier, while others will fix your catalytic converter for a lot cheaper. Your task will be to find a shop that will replace the converter for the cheapest price.

How To Clean A Catalytic Converter?

Catalytic converters that are clogged up can also be cleaned pretty easily. There are many solutions out there on how to clean a catalytic converter, and there are also some products that we are going to discuss in this section.

Drive It On The Highway

A drive on the highway is a good way to clean your catalytic converter. Catalytic converters are clogging up because most of the time, you drive only for short distances. Doing so will cause the materials that are inside of the catalytic converter to not reach up to its operating temperature.

This will cause the catalytic converter to fill up with carbon and prevent the exhaust gasses to escape. So, the best solution is to drive your car on the highway. Drive it for at least 10-15 minutes at higher RPMs. Roughly 4000-4500 RPM will make sure that all the debris inside will burn and dissolve. In the end, you are going to have a perfectly working catalytic converter


This CataClean solution for clogged catalytic converter reportedly works. You just need to pour it into your tank and the solution will do its magic. This is a good method to combine with the first fix of driving your car on the highway. This will make sure that the catalytic converter is cleaned thoroughly.

Signs Of A Bad Catalytic Converter

Just pour some of this solution into your tank and give it a good highway run. After this, check the results. There will be no more check engine light on the dash, and your car will run like new again.

Clean The Converter Manually

Another good solution is to clean the catalytic converter manually. This involves a lot of work but it’s probably more effective than the other two methods if your catalytic converter is extremely clogged.

For this method, you will need to take your catalytic converter out from your car and clean it manually. Many people use different solutions, as some use soap and water while others resort to lacquer thinner. It’s important to place the catalytic converter and leave it immersed in either mixture and leave it overnight. This will give the solution the time it needs to work and dissolve the debris left behind.

In the morning, you can get a high-pressure hose and clean it off with water. Make sure you have enough pressure to remove all the dirt inside the catalytic converter. Be persistent, because this can last for a while until all of the debris is removed.

After you finished cleaning you can mount the catalytic converter back on the car and start enjoying your car more than you used to.

What If I Continue Driving Like This?

If you continue driving with a faulty catalytic converter, it’s not good for you and your car. You may get check engine lights and cause your car to fail prematurely. When the catalytic converter is clogged, many components inside of the engine will suffer and can go bad. In addition, the catalytic converter itself can decompose and destroy itself. Buying a new catalytic converter is pretty expensive as we laid out before.

Be Aware Of Thefts

Also, you need to be aware of thefts. You shouldn’t park your car overnight in some shady neighborhoods or dark alleys. These converters are easily stolen by burglars that sell them on the black market for their precious metals.

Many catalytic converters thefts happen each day and you never know if you will be that guy, so it’s better to be safe than sorry.


We’ve covered a lot in this article. We have learned of what catalytic converters are. Moreover, we know now what their role is, and from which materials are they fabricated.

Then, we’ve covered all of the warning signs of a bad catalytic converter. There are plenty of early symptoms that are exhibited when it comes to this issue and most of them are fairly easy to recognize before you can later diagnose the issue.

The most important thing when you are having a catalytic converter that is clogged is to not prolong the cleaning process. The longer you wait, the more expensive the repair bills will be. At the very worst, you will have to buy a new one.

And finally, we covered some of the methods on how to clean a catalytic converter. Some of them are fairly simple, but the more complicated solutions that require a full catalytic converter removal will be a more permanent and robust fix. With this guide, you can be sure that your catalytic converter will not fail you any time soon.

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  • Frank Says

    Very interesting and helpful! It covers a lot and helped me understand the issues with my catalytic converter. Unfortunately we don’t find around here Cataclean, a friend recommended to use Sea Foam hig mileage.
    Thank you very much!

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