How to Unclog a Catalytic Converter

Catalytic converters play an essential part in keeping the environment as safe as possible from poisonous and otherwise harmful gasses that come out from the exhaust system. As of the mid-70s, these devices became mandatory in all cars produced and sold in the United States, and the basic construction remains unchanged to this day, although it has been perfected over decades. 

A catalytic converter is positioned between the exhaust manifold and the muffler. It is located underneath the car, closer to its rear end.

A catalytic converter existed long before it became mandatory in the United States in 1975. Since then, it has been used by manufacturers as a line of defense against air pollution with both gasoline and diesel engines. Regardless of fuel, a catalytic converter works under the same principle with a goal to reduce the emission of toxic byproducts of combustion.

A bad catalytic converter not only harms the environment but also decreases the performance of your car or can even stop it from working. So today, I’m going to talk about clogged catalytic converters, how to diagnose them, and how to fix them before extensive damage destroys them and harms your car.

How to unclog catalytic converter.

How Do Catalytic Converters Work?

As you already know, various harmful gasses are a byproduct of the engine’s combustion. Simply speaking, precious metals inside the converter act as catalysts in a chemical process that oxidizes carbon monoxide into carbon dioxide and unburnt fuel into carbon dioxide and water.

The first mass produced catalytic converters were two-way converters, while modern three-way converters also control the emission of nitric oxide and nitrogen dioxide, harmful gasses that get reduced to nitrogen alone.

What Are the Most Common Catalytic Converter Problems?

Even though a catalytic converter is a simply constructed device designed to withstand exposure to high temperature, it is still prone to physical damage and breaking. A badly clogged catalytic converter can cause your car to stop working. That’s why it’s important to have it in check and react fast as soon as the first symptoms appear. 

The replacement of a catalytic converter is expensive due to the fact that this part of your car is literally filled with precious metals. Gold, rhodium, palladium, and platinum are used as catalysts which help purify the exhaust fumes.

Since a catalytic converter is located on the bottom side of the car, the most common catalytic converter issues include physical damage. 

Right after that, there’s a clogged catalytic converter. A catalytic converter can clog when the engine is working improperly. All unburnt fuel and oil can clog the honeycomb structure of the converter, leading to numerous other complications over time. 

If a catalytic converter is clogged for a longer period of time, excessive heat of trapped exhaust fumes could melt and fuse the catalysts, making the catalytic converter irreparable and completely destroyed.

In theory, you could drive your car with a clogged or damaged catalytic converter indefinitely. However, if you live in a place with regular smog checks, you could be fined, or your car could be banned from traffic due to excessive pollution generated by its faulty exhaust system.

Unclogging a catalytic converter (car exhaust system)

Clogged Catalytic Converter Symptoms

There is no definite way to know whether your car’s catalytic converter is clogged without removing it and opening it. However, this procedure requires a handful of tools and some mechanical knowledge and isn’t recommended for anyone. If you have an equipped garage and needed knowledge, you can do it yourself.

As I previously mentioned, unburnt fuel is the main cause of a clogged catalytic converter, so diagnosing your engine is the first step towards diagnosing a bad converter. 

  • If your engine misfires or you have exhaust valve issues, you’re most likely on your way to having a clogged catalytic converter. So check your spark plugs and valves to eliminate one cause of catalytic converter damage.
  • Also, if your car is running on rich fuel and air mixture, massive amounts of unburnt fuel are another step towards a plugged catalytic converter.
  • If your car’s engine is leaking oil, any oil that burns in the catalytic converter is directly harming it. 
  • Worsened fuel economy is another way to diagnose a bad catalytic converter. It also leads you to the previous point: running on rich fuel mixture.
  • On the other hand, lean fuel mixture can also damage the catalytic converter if not treated on time.
  • Rough idle and rough acceleration are symptoms which also point to a faulty or clogged catalytic converter.

Some catalytic converter issues are best diagnosed when you find yourself underneath your car

  • Physically inspect the catalytic converter. First, any distortion of the housing will point out to physical damage. Since a catalytic converter is located on the bottom side of your car, any road debris, curbs, or larger bumps could cause damage, internal and external. Any rattles inside the catalytic converter point out to the damage as well.
  • If your car’s catalytic converter housing is discolored, that might be a sign of an overheated clogged catalytic converter.

Finally, the last and the most tech-savvy DIY method is via the diagnostic tools

  • Provided that you have an OBDII reader and an appropriate app, you can diagnose your car by yourself. The PO420 code points to a faulty catalytic converter. The efficiency of a catalytic converter is measured via two oxygen sensors: one in front of it and one behind it. If you’re suffering from a faulty catalytic converter, the second O2 sensor will cause the PO420 code to activate. 

Treating a Clogged Catalytic Converter

Before unclogging the catalytic converter of your car, it’s important to sort out issues that lead to it being clogged in the first place. Cleaning or replacing the catalytic converter won’t fix the problem as a whole. On the contrary, you’ll end up clogging and damaging the catalytic converter again, or even worse, you’ll damage a new one.

  • The first and the easiest way to unclog a catalytic converter is by taking your car to a highway. Drive your car for a couple of miles, and when there’s no one behind you, brake to quickly reduce the speed of your car. Repeat the acceleration and deceleration process a few times. If you notice that your car has regained its usual performance, you’ve unclogged the catalytic converter. Bear in mind this is a temporary solution that works only when there’s nothing but the lightest clogging.
  • The other way to unclog a catalytic converter without removing is by using a special product designed to clean it. Make sure to inspect your catalytic converter beforehand, as this method will only work with light clogging. If that’s the case, tap the Oxicat solution into the fuel tank of your car and follow further instructions. If appropriately used, Oxicat will clean up O2 sensors and the catalytic converter itself. This is also a temporary solution that helps reduce clogging of the catalytic converter but won’t stop further clogging if the main cause hasn’t been treated.
  • If you have the resources to unclog the catalytic converter yourself, make sure to properly inspect it and wash it with a mixture of hot water and degreaser. If the converter has no damage, cleaning it should be a fairly simple process. However, you need to be sure that it’s not damaged and that you know how to unmount it and mount it back to its place.
  • If your catalytic converter is too clogged or if it has suffered significant physical damage, it’s the best that you replace it. This is a costly procedure, but your old catalytic converter could be sold to scrap to lessen the total cost of the process.


A catalytic converter is an important part of every car with an internal combustion engine, and even though it’s simple in construction, it is costly due to precious metals sitting inside of it.

You can unclog a clogged catalytic converter only in case of light damage. Ignoring the issue will inevitably lead to a failed catalytic converter that could only be replaced.

Finally, and most importantly, a clogged catalytic converter is an issue by itself. In addition to that, it’s also a clear sign of other problems your car is suffering from. That’s why it’s of utmost importance that you diagnose the reason behind a clogged catalytic converter. 

Cleaning or replacing a faulty catalytic converter while ignoring the causes won’t solve the issue in the long run. It will leave you with another clogged catalytic converter that will again have to be replaced in another costly procedure.



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