Informational Guide

How To Unclog A Catalytic Converter

When a catalytic converter is clogged, it can lead to performance issues. We show you how to tell if it’s clogged and how to unclog a catalytic converter.

The catalytic converter is a vital part of your vehicle's exhaust system. It's necessary for cleaning the exhaust gases from your vehicle before they hit the environment.

When the catalytic converter is clogged, it can lead to performance issues. Instead of worrying about an expensive repair, we will show you how to unclog a catalytic converter and how to tell if a catalytic converter is bad.

How does a catalytic converter work? Your car engine makes pollutant gases that can be harmful to the environment. To reduce pollution, the catalytic converter uses a catalyst to produce a chemical reaction and change the gas's molecular structure before it hits the air.

The catalytic converter itself is just a large metal box that is bolted under your vehicle. It contains two pipes that come out, one for input and the other for output.

There are two stages that occur within the catalytic converter, the reduction catalyst and oxidation catalyst. First, the reduction catalyst removes nitrogen oxide by breaking it down to nitrogen and oxygen. After that, the oxidation catalyst oxidizes the carbon monoxide into carbon dioxide.

How To Unclog A Catalytic Converter

Most Common Types Of Catalytic Converters

  • Two-Way Catalytic Converters 
    Exhaust gases flow through the catalyst made of precious metals. As the conversion occurs, the gases increase in temperature, which makes them hotter as they leave the converter. Heat shields are required with these units for protection.
  • Three-Way Catalytic Converters 
    The catalyst chemistry stores and releases oxygen with the help of the O2 sensors. With proper storage and release, there is a greater reduction of emissions. If the system isn't working as it should, the onboard computer alerts the driver.
  • Three-Way Plus Air Catalytic Converters 
    At the front of the converter, precious metal rhodium is used to reduce the NOx emissions into N2 and O2. There is a second substrate that is coated with precious metals to oxidize the HC and CO into CO2 and H2O. This system doesn't run efficiently and has been mostly phased out since the 1980s.

How Can You Tell If Your Catalytic Converter Is Clogged? (Symptoms)

Do you know how to tell if the catalytic converter is clogged? We review some of the most common symptoms that show you how to tell if your catalytic converter is clogged.

  • Problem with the engine performance 
    When the catalytic converter is clogged, it creates backpressure. This imbalance negatively affects the air/fuel ratio and causes performance problems.
  • Issues on fuel efficiency 
    Because less air can get to the engine, you will notice a drop in fuel efficiency.
  • Dashboard warning lights 
    On modern vehicles, the computer monitors the exhaust system and alerts you if there is a problem.
  • Failed emission test 
    If the catalytic converter isn't breaking down the exhaust properly, your car could fail its emissions test.
  • Rotten egg smell 
    When the catalytic converter is no longer working properly, you will start to smell sulfur.

Checking & Diagnosing A Clogged Catalytic Converter

Before you learn how to unclog a catalytic converter without removing it, you must be sure there is a problem. Here are some steps to diagnosing your catalytic converter.

Vacuum test

To perform a vacuum test, you will require a vacuum gauge. Most people don't have these, but shops do. Set the car to Park and apply the parking brake. A friend can attach the vacuum to the direct intake manifold port. Let the vehicle idle until it reaches operating temperature.

You want to see a reading of 18 and 22 in-Hg. When you step on the accelerator and reach 2500 to 3000 rpm, any drop in pressure that doesn't immediately return means there is a blocked catalytic converter.

Back Pressure test

For this test, you must get a back pressure gauge. Take off the front oxygen sensors and put the gauge on in their place. Start the car and watch the gauge. If it is between 0-3 psi, it is normal. However, readings beyond 8 psi indicate a clogged catalytic converter.

Temperature test

Grab your kitchen or infrared thermometer for a simple test. Start your car and let it warm up. With the vehicle in Park on a flat surface, check the temperature coming out of the inlet pipe. Do the same test on the outlet pipe. If the front is the same temperature as the outlet, there could be a problem.

Use Of An OBD Scanner

When there are issues with the exhaust system, including with the catalytic converter, the computer might set a diagnostic trouble code. You can use the OBDII scanner to determine what the DTC is and how to resolve it.

How To Unclog A Catalytic Converter Without Removing It

Unclogging a catalytic converter without removing it isn't as difficult as you might think. Plus, learning how to clean a catalytic converter doesn't require any special skills. Instead of learning how to remove a catalytic converter, use these steps to figure out how to fix a catalytic converter without replacing it.

  • Find a high-quality catalytic converter cleaner.
  • Fill up the fuel tank as per the instructions on the cleaner.
  • Pour the container into your fuel tank.
  • Run the vehicle, so the solution mixes with the fuel. You will want to drive for at least 30 minutes.

At the end of the drive, the car should be accelerating better. If it doesn't work, you will need to learn how to unclog a bad catalytic converter, which might require removing it.

Unfortunately, using a cat cleaner only helps you learn how to fix a clogged catalytic converter when the issue isn't severe. Thankfully, when you examine how much to unclog a catalytic converter, you see that there wasn't a lot of money spent trying.

How To Unclog A Catalytic Converter By Removing It

If the clog is severe, you will need to take additional steps when learning how to clean a catalytic converter. In this case, you will need to understand how to clean out a catalytic converter by removing it. Basically, you are learning how to gut a catalytic converter.

  1. 1
    Make sure the exhaust is completely cool.
  2. 2
    Use a floor jack to lift up the car and secure it with jack stands.
  3. 3
    Remove the oxygen sensors.
  4. 4
    Loosen the bolts on the catalytic converter and remove it.
  5. 5
    If the converter is making a rattling sound, there's nothing more you can do.
  6. 6
    Otherwise, use a pressure washer to clean the converter at lower pressure.
  7. 7
    Use a degreaser and hot water to clean it.
  8. 8
    Rinse it off with the pressure washer on low.
  9. 9
    Install the converter once it has dried completely.
  10. 10
    Install the oxygen sensors.
  11. 11
    Test drive the car.

Replacing Your Cars Catalytic Converter

If you learned how to clean a clogged catalytic converter and nothing seems to help, you might need to replace it. How long does it take to replace a catalytic converter? It depends on your vehicle type. How much does it cost to replace a catalytic converter? The part alone can run you more than $1,000.

To replace it yourself, simply follow the same steps we outlined for removing it to clean it. Learning how to take off a catalytic converter requires you to remove a few bolts that could be tight.

Then, instead of cleaning it, reinstall your new catalytic converter. You should notice an immediate difference in performance and responsiveness.

How To Tell If A Catalytic Converter Is Clogged

People Also Ask (FAQs)

How much is a catalytic converter worth scrap?

Catalytic converter scrap prices range from $100 to $350, depending on what type of model you have. The precious metals in the catalytic converter make it valuable, which is why this part is commonly stolen from vehicles.

Can a car run without a catalytic converter? How long can you drive with a bad catalytic converter?

The car doesn't need a catalytic converter to run. However, your vehicle will fail its emissions testing and it is polluting the air unnecessarily, so you should fix it immediately.

What happens if I don't replace/fix a catalytic converter?

Eventually, the bad catalytic converter can cause the exhaust to become plugged, which will affect the engine performance of your vehicle. When the engine isn't optimized, its life is severely diminished.

What is the best catalytic converter cleaner?

Many people recommend Cataclean when learning how to unclog a catalytic converter. However, there are also enthusiasts that recommend Sea Foam as an all-around good cleaner, so you will need to decide which is better for your vehicle.

How does a car sound without a catalytic converter?

After you remove the catalytic converter, you will notice a deeper exhaust note than when it was installed. Some people prefer this, which is why they remove it, but you can get a better tone by simply upgrading your vehicle's exhaust system.

What is the cheapest way to clean a catalytic converter?

How much does it cost to unclog a catalytic converter? If you use one of the cleaners we recommended, it won't cost much. However, if that doesn't work, you will be forced to replace it, which can be costly.


We have taught you how to check for a clogged catalytic converter and looked at some methods to fixing it. With our steps, you can get your catalytic converter running its best so you can avoid costly repair bills.