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Can You Fix a Catalytic Converter Without Replacing It?

Vehicle underbody with the catalytic converter and resonator visible on the exhaust system

Replacing a catalytic converter is a very expensive problem to have. It’s an essential part of your vehicle, and you might feel trapped and frustrated now. The good news is that you came to the right article — I’m going to teach you about catalytic converters, some damage to look for, and whether or not you need to replace them.

The good news is that you can fix a catalytic converter without replacing it, effectively saving thousands of dollars. Instead, use a degreaser, pressurized water, and a fuel additive to clean up the insides of your catalytic converter. Another option is to accelerate quickly when it’s safe to do so, then slow down and repeat the process to heat up the cat and melt away trapped debris.

The Role of a Catalytic Converter

You might have heard of catalytic converters in the past, but what do they do? It’s the most expensive and essential part of your exhaust system.

Your exhaust system pumps toxic chemicals away from you. The chemicals are created in the engine and they’re the byproduct of the miniature explosions going on under the hood.

The exhaust system will take these fumes away from your engine, scrub out the toxic chemicals, make the noise quieter, then get rid of the smoke behind your car through the exhaust pipe or tailpipe.

The main role of the catalytic converter is to get rid of the toxic chemicals within the smoke. Without a catalytic converter, breathing in fumes from your tailpipe could be fatal.

How does it do that? Through precious metals and chemistry. To avoid the complicated science going on, I can simplify the process into this series of events:

The toxic smoke is blown through your catalytic converter and passes through a honeycomb maze that’s lined with precious metals like platinum or palladium. As the smoke goes through this maze, harmful compounds are simplified into harmless elements like nitrogen, steam, and carbon dioxide.

On the other end of this honeycomb is a pipe that sends the new elements through the rest of your exhaust system (specifically, to the muffler and then the tailpipe).

Illustration diagram of how a catalytic converter works on the exhaust system of a vehicle car - higher resolution

How a Catalytic Converter Might Break

In a second, I’ll get into some diagnostic steps. In this section, I want to be a bit more general. I want to discuss different ways that a catalytic converter might break.

In a brand-new, ideal catalytic converter, the operation is simple enough: toxic smoke enters from one end of a sealed tube. It’s forced through the honeycomb pattern I mentioned earlier, then safe smoke exits the other end, through another sealed tube.

Within that assembly, there are certain issues that will hurt the functionality of the catalytic converter:

  • A cracked pipe. Cracks mean that smoke can escape and bypass the catalytic converter altogether. It also can lead to other mechanical problems and backflow issues.
  • Damaged precious metals. If there’s damage to the honeycomb pattern, then the incoming toxic gas won’t be cleaned enough before exiting the catalytic converter. Engineers factor in how much precious metals are used when they calculate the performance of a catalytic converter.
  • Sealing problems. On either end of the pipe and the cat itself, there are seals. If the seal is broken anywhere, then smoke can escape before being polished and having the toxins removed.
  • Clogs. No, I’m not talking about the cool shoes that Danish people wear. If pollutants and particles clog up the honeycomb pattern within the converter, then the airflow will be restricted. This can cause backups and performance issues.

Signs Your Catalytic Converter Has a Problem

Before getting too far, I should explain some diagnostic steps. These are common signs that your catalytic converter is having an issue.

Rattling While Engine Is On

If you ever hear rattling, it’s a bad sign. Rattling means that something is broken, not attached correctly, or something came loose.

In this case, it might mean that precious metals broke apart in your catalytic converter. The broken-off chunk of metal will just rattle around while smoke enters the pipe.

The problem is that this precious metal is no longer doing anything. Smoke will flow through the converter without being appropriately scrubbed and cleaned.

It’s also possible, but less common, that the fasteners holding your catalytic converter in place have come loose. In this case, the seal between the exhaust line and the cat has been broken.

The Housing Is Warped, Discolored, or Cracked

It’s always a good idea to do a visual inspection of mechanical pieces on your car. When you’re looking at the catalytic converter, you want to look for any signs of damage or discoloration. This is easiest to do with the catalytic converter removed, but it’s possible to see what’s going on by simply jacking up your car, crawling underneath, and using a flashlight.

If you drove over road debris that bounced up and hit your catalytic converter, you might experience some damage. In some vehicles, the catalytic converter is one of the lowest-hanging parts on the undercarriage. Bottoming out after a bump, going over a curb, or when hitting a pothole might mean that the cat hits the road. This can lead to a ton of damage to the cat housing.

It’s best to check the catalytic converter when the car is turned off. That way, you’re not exposed to toxic gases that are leaking out of the housing.

Close up from the bottom of the car of the catalytic converter on the exhaust pipe

Issues Starting or Accelerating

The next problem to look at is a little tougher to understand without getting into the science. I’ll keep it brief, so I don’t bore anyone to sleep.

Your car needs a certain amount of airflow from the engine to the tailpipe — think of it like water coming from your garden hose. If there are kinks in the hose, then water won’t come out as fast, it might spurt, and pressure will build up. With a big enough kink or blockage, the water will stop altogether.

This same sort of fluid physics is going on under the hood. Your engine needs to “breathe” since oxygen is one of two compounds the engine needs in order to convert fuel into motion.

Your car’s exhaust system is the only way an engine can “exhale” since it’s the only line going from the engine block to the outside world (otherwise, toxic gas will come out of your hood, and you’ll be in a moving death machine).

If your catalytic converter is blocked, clogged, or damaged, then the airflow will be restricted. Your engine suddenly can’t “breathe” as well, and your performance will suffer. Namely, stomping the gas pedal won’t have the huge acceleration that you’re used to. Getting up to speed will be more challenging, and you can run into issues trying to start your car.

There are also some safety features that might electronically prevent your modern car from starting if your catalytic converter isn’t running correctly. There are typically two oxygen sensors installed for a single catalytic converter along the exhaust on both sides of the cat to measure the difference in how much un-burned oxygen there is. These are called downstream and upstream o2 sensors.

The upstream o2 sensor is typically located before the catalytic converter to measure the air-to-fuel mixture. The downstream o2 sensor can be located on the other side of the catalytic converter closer to the rear to measure the oxygen after it passes through the cat. If the difference isn’t big enough, an alert is sent to the computer onboard your car and your starter will be locked down and prevented from working.

You Smell Rotten Eggs

Speaking of leaking gasses, you should keep your nose open when troubleshooting the catalytic converter. Sulfur compounds are a byproduct of your engine’s combustion process. As you might know, sulfur has a nasty smell that’s skin to rotten eggs.

If your car is running and you smell something like rotten eggs, you should immediately turn your car off and troubleshoot your exhaust system.

If you smell this rotten fragrance, it means that the seal is broken somewhere. It could be a gasket on either end of the catalytic converter that failed, a crack in the housing, or damage to the exhaust line upstream of the cat.

Regardless of where the leak is, you’re smelling toxic gasses. It’s never a good idea to overexpose yourself to this smoke, so make sure you aren’t around your car if it’s running before you fix it.

Close up of smokey dual car exhaust pipes at sunrise in the morning

The Problem with Catalytic Converter Replacements

Your catalytic converter comes in a single housing that’s relatively easy to uninstall and reinstall. As far as DIY repairs go, it’s honestly one of the easier ones.

The issue isn’t with access or removability of your cat — it has to do with the price. If you have a modern car, you can expect to spend thousands of dollars on a new catalytic converter.

If you’re like me and your eyes are currently bulging out of your head, I have even worse news: you can’t cheat and lie your way out of the replacement. Your car is constantly checking if the cat is working, there are laws that require your cat to work, and inspectors will make sure your cat is working before deeming your car street-legal.

If you just ignore your broken catalytic converter, then you’ll be driving an illegal car that will earn you a huge ticket when you get found out. Not to mention you’ll be putting your life at risk every time you start your car.

It’s not worth it, and you need to fix the cat as soon as possible.

Can You Fix a Catalytic Converter Without Replacing It?

All of the information I covered is to answer a single question: can you fix a damaged or broken catalytic converter without replacing it?

You can fix your catalytic converter without replacing it as long as the damage isn’t too severe or too far gone.

Ways to Fix Your Catalytic Converter

There are three major ways to repair your cat without replacing it:

Add In a Fuel Additive

Fuel additives are cleaners that go into your vehicle’s gas. They can be added every once in a while, and they’re known to boost your performance and clean your catalytic converter.

I highly recommend a very popular fuel additive which is the CATACLEAN. It’s specifically aimed at cleaning the exhaust system and the catalytic converter.

Cataclean 120007 Complete Engine, Fuel and Exhaust System Cleaner, 473 Milliliter
Cataclean Fuel and Exhaust System Cleaner

Give it a “Wash”

As odd as it seems, you can potentially wash out your clogged catalytic converter with a pressure washer. Remove the catalytic housing, and shoot pressurized water through the inlet then hit the outlet after.

If it’s really bad, you might want to mix the degreaser with warm water, pour it into a container, and leave your catalytic converter in there to clean up before pressure washing.

Drive Your Car Hard

Another way to clean your catalytic converter is to heat it up a bunch. One way to do that is to drive hard. Go on a long, empty stretch of road and hit the gas pedal hard, and accelerate up to the speed limit quickly. Then brake back to a manageable speed and repeat the process.

This sudden flux of gas going through the exhaust system will heat up your cat and can burn away residue that’s stuck inside of it.


Now you know how to fix your catalytic converter without replacing it. My tips should save you a few thousand dollars and a big headache.

For more car tips and DIY guides, explore the rest of my site. Leave a comment below if this guide helped you and be sure to check out my list of recommended car products.

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How to Fix a Catalytic Converter (Without Replacing It)

Ernest Martynyuk

An automotive enthusiast who's been tinkering with vehicles since I was 15-years old. Repairing automotive electronics has been my main job for over a decade now and have a passion for everything technical regarding cars.

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