You can unclog your car’s catalytic converter with a catalytic converter cleaner or by removing the part to pressure wash and degrease it before reinstalling it.

Ominous black smoke, the smell of rotting eggs, extreme heat coming from below—not quite hell but close to it, these are all signs of a clogged catalytic converter. Catalytic converters are crucial to both your engine’s performance and the environment, so it’s beneficial to know how you can unclog one if you ever need to.

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Unclogging a catalytic converter

A catalytic converter is a device in your vehicle’s exhaust system that converts harmful, polluting exhaust gasses into less harmful emissions.

When it’s clogged or otherwise damaged, the catalytic converter can’t do its job as well and releases more harmful substances into the environment. It will also decrease your car’s fuel efficiency and has the potential to damage your car’s engine.

Before diving into the “how” of unclogging a catalytic converter, it’s a good idea to make sure the catalytic converter is not damaged beyond repair so you don’t do all this work for nothing. Check with a mechanic if you’re unsure!

When you get confirmation that your catalytic converter is simply gummed up with a bit of debris and not falling apart, you can unclog it in two ways: removing it and cleaning it, or not removing it and adding a catalytic converter cleaner to your fuel system.

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Removing to clean

If you choose to remove the part to clean it and then reinstall it, here’s what you’ll need:

Automotive degreaser

Penetrating oil

Jack and jack stand

Impact wrench

Pressure washer

Make sure your exhaust system has had time to properly cool down before you begin work so you can avoid burns. Once you’re sure you aren’t risking burned skin, raise your vehicle on jack stands and remove the oxygen sensor.

Next, apply the penetrating oil around the bolts holding the catalytic converter in place to loosen them. Then, remove the catalytic converter.

Once the part is removed, give it a shake to listen for any rattling sounds. If you hear something rattling around inside the converter, it is most likely damaged beyond repair and you’ll need to look into replacing the part.

If you don’t hear anything, grab your pressure washer set at a low-pressure setting and wash out the catalytic converter. There will likely be bits of debris that fall out, so be sure to properly dispose of them.

When you’re satisfied with the clean, allow the part to dry completely before reinstalling your catalytic converter. Complete the process by reinstalling the oxygen sensor, and you’re done!

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Cleaning without removing

If you’d rather clean the catalytic converter without removing it, here’s what you’ll need:

Catalytic converter cleaner

Funnel (optional)

Catalytic converter cleaners typically come as a fuel additive that you simply pour into your fuel tank. When choosing a cleaner, make sure it works for your specific vehicle’s systems and read the reviews! There are a lot of brands out there, so narrowing them down will help you make the selection.

Here are a few cleaner options to help you along:

Oxicat Oxygen Sensor & Catalytic Converter Cleaner

, available from Amazon for $13.45

Chevron Techron Concentrate Plus Fuel System Cleaner

, available from Amazon for $12.95

Motorkote Catalytic and Exhaust Treatment Emissions Control Catalytic Cleaner

, available from Amazon for $19.00

Different cleaners may have different fuel level needs so be sure to read the instructions on the specific cleaner you purchase. Typically, you’ll want to add the cleaner when you’re at about a quarter tank of gas.

After adding the cleaner at the appropriate time, drive around on the cleaner/fuel mix until your tank is empty—or just about—and it will have circulated through the exhaust system to clean out your catalytic converter.

You’ll be able to tell if the cleaner had some success if your exhaust smoke is lighter in color, not as smelly, and if your car accelerates quicker.

It’s important to note that catalytic converter cleaners will not sufficiently work if your catalytic converter is particularly gummed up with debris. They aren’t a fix-all past a certain point.

Ultimately, preventative maintenance is crucial to keeping a healthy catalytic converter. One of the most effective prevention methods is a regular oil change routine. This will help keep your fuel and oil systems clean and in proper working order.

It is also recommended that you switch to a high-mileage oil once your car reaches 75,000 miles and above.

MORE:

How to choose the best gasoline or fuel for your car

Symptoms of a clogged catalytic converter

Maybe you’ve come to this article without the urgent need to clean your catalytic converter, but you suspect it may become an issue soon. Congratulations—you’re just ahead of the game on that whole preventative maintenance thing!

In any case, let’s go over what to watch out for if your catalytic converter is having problems:

Engine issues: Your engine won’t start, it sputters and stalls out, or you notice an engine knock at slower speeds.

Fuel efficiency issues: Your fuel efficiency takes a dive because your engine has to work harder and consume more fuel due to a block in the catalytic converter.

Failed vehicle emission test: Perhaps the most telling sign. Your vehicle fails a vehicle emissions test and is kicking out more harmful substances than regulatory standards.

Foul smell/rotten egg smell: The smell of rotten eggs means there is sulfur, one of the harmful gasses that the catalytic converter tries to convert to something less harmful, in the exhaust system.

Your check engine light comes on: Your car’s diagnostic systems alert you to an issue with one of your components. Check on the catalytic converter.

MORE:

How to pass emissions testing

Diagnosing a clogged catalytic converter

Hopefully, you read through those symptoms and can now cross “clogged catalytic converter” off your list of potential car problems. If not, you’ll want to properly diagnose the problem. There are a few ways you can do this. You can find the tools for the job online or in your local auto store.

Vacuum test your catalytic converter

For this diagnostic method, you’ll need a vacuum gauge and a driving partner.

Turn your vehicle off.

Attach the vacuum gauge to a direct intake manifold or another similar direct vacuum line.

Turn your vehicle on and allow it to warm up to its normal operating temperature. The vacuum gauge should show a value between 18 and 22 inches of mercury (in-Hg).

Go for a drive and keep up a speed between 2500-3000 RPM. Either you or your driving partner—whoever isn’t the active driver, ideally—will be paying attention to the vacuum gauge.

The gauge reading should decrease and then return to its former level very quickly.

If you notice that the reading doesn’t reach its former level in just a few seconds, your catalytic converter may be clogged.

MORE:

How to test an oil pump

Temperature test your catalytic converter

For the temperature test, you’ll need an infrared or kitchen thermometer and a jack and jack stands (optional). Here’s what to do:

Park your car on level ground and let it idle until it reaches its normal operating temperature. This can take between five and 20 minutes.

Take the temperature of the inlet pipe connected to the front of the catalytic converter and note it somewhere. You may have to jack up your car to get under it properly.

Take the temperature of the outlet pipe connected to the rear of the catalytic converter and note it somewhere.

The outlet pipe temperature should be 50 to 100 degrees Fahrenheit hotter than the inlet pipe. If the two temperatures are reading similarly or the inlet temperature is higher, it’s a good indication that you have an issue with the catalytic converter.

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Back pressure test your catalytic converter

The final test is a back pressure test. For this, you’ll need a back pressure gauge.

While your vehicle is off, change out the front oxygen sensors of the exhaust system with the back pressure gauge.

Turn your vehicle on and check the back pressure gauge reading.

You should see a reading between 0 and 3 PSI. If you’re getting higher readings, your catalytic converter is likely clogged.

MORE:

Does car insurance cover engine failures

Securing affordable car insurance

Replacing a catalytic converter can be pretty expensive, but keeping up with regular oil changes can prevent you from having to spend that money in the first place.

There are other great ways to cut back on car expenses, too. To save money on

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Do I have to replace my catalytic converter if it’s clogged?

It depends on how clogged it is! If you catch it early enough, you should be able to simply clean the catalytic converter by either removing and washing it out, or running a catalytic converter cleaner through your fuel systems.

If it is significantly clogged, however, you will likely have to replace it.

Can you unclog a catalytic converter?

Yes, in many circumstances, you can unclog a catalytic converter. You can either remove the part and clean it out or use a catalytic converter cleaner. If these options don’t work, your converter may be too clogged to repair.

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