5 Steps to Clear a Clogged Catalytic Converter by Yourself

Is your car struggling to accelerate? Does your car smell like rotten eggs?

If you have an older car with the original catalytic converter, you may be able to freshen up the smell and pick up some power by cleaning your catalytic converter.

What is a Catalytic Converter?

A catalytic converter is an an emissions device that converts many harmful exhaust gases into safer substitutes. For instance, carbon monoxide and unburnt hydrocarbons are converted to carbon dioxide (the same stuff you exhale) and water.

Inside a catalytic converter, there are several precious metals which are designed to speed up the breakdown of these toxic gases. These metals are known as the catalyst. The catalyst is arranged in a honeycomb pattern to maximize surface area as the air flows through the exhaust system.

Why Would a Catalytic Converter Need Cleaning or Replacement?

catalytic converter interior

Over time, carbon builds up inside an engine as a result of incomplete combustion. Over thousands of miles, some of this carbon will also build up in the exhaust system.

The catalytic converter is particularly prone to carbon buildup, as this build up could clog the catalytic converter or reduce its efficiency.

Symptoms of a Dirty Catalytic Converter

check engine light

Check Engine Light

Catalyst efficiency is measured using two oxygen sensors – one upstream and one downstream of the catalytic converter. If the two O2 sensor signals don’t match what the ECU is expecting, one of these codes may be thrown.

The following is a list of common catalytic converter codes. Any code relating to “catalyst efficiency” may warrant a cleaning or replacing of the catalytic converter.

  • Bank 1 catalytic converter codes: P0420, P0421, P0422, P0423, P0424, P0425, P0426, P0427, P0428, and P0429.
  • Bank 2 catalytic converter codes: P0430, P0431, P0432, P0433, P0434, P0435, P0436, P0437, P0438, and P0439.
Note:  Not all engines have two banks. For instance, a straight 6 has all cylinders in a line. If you see a code for bank 2 in an inline engine, the code may be referring to the downstream oxygen sensor.

Sluggish Acceleration

A clogged catalytic converter is a restriction in the exhaust system. Exhaust restrictions create back pressure that reduces acceleration. Reduced acceleration occurs because the vehicle has to work harder to push exhaust through the system.

If your car feels a lot slower than it used to, try cleaning or replacing the catalytic converter.

Rotten Egg Smell

Have you noticed how exhaust from classic cars tends to smell a long stronger than modern cars? The gases produced by a combustion engine smell pretty bad without a catalytic converter to make them less harmful.

If you notice a foul smell from the exhaust, this is another indicator that your catalytic converter needs attention.

Should You Clean or Replace Your Catalytic Converter?

symptoms of a bad catalytic converter

When you’re trying to decide if you should clean or replace your catalytic converter, there are a few things you might want to consider.

The Age of the Vehicle

The catalyst is made of precious metals such as platinum, palladium, and rhodium. These metals break down over time as they do their part to keep the environment clean. If you have over 100,000 miles on your catalytic converter, you will probably want to replace the catalytic converter instead of clean it.

Your Warranty

If you have an active warranty on the vehicle, check the terms of the warranty. Working on your own catalytic converter may void a portion of your vehicle’s warranty, leading a warranty claim to be denied.

Your Local Laws

There are a lot of laws surrounding emission control devices, and these laws vary from state to state and country to country. If you decide to remove your catalytic converter, it’s best to check with your local laws to make sure you will pass inspection.

You can’t just take the catalytic converter off, either. Nearly any state that requires an inspection will fail you if you’re missing a catalytic converter.

See Also: 5 Cars Least Likely to Suffer Catalytic Converter Theft

How To Clean Your Catalytic Converter (With an Additive)

best catalytic converter cleaner

The following products are easy and relatively inexpensive to try. It generally doesn’t hurt to try an additive before moving on to more invasive steps, like a deep clean or replacement.

Intake Spray

There are several products on the market that can help clean your catalytic converter without unbolting the exhaust. One such example is Liqui Moly 8931 Catalytic-System Cleaner.

Liqui Moly is a trusted name in the automotive industry that offers products ranging from engine oils to heavy duty cleaners. Simply spray the catalytic cleaner into the intake tract at short intervals while the engine is running at a moderate speed (2,000 to 3,000 RPM). Follow instructions on the can for best results.

Fuel Additive

There are also fuel additives on the market that claim to clean the catalytic converter. You could try a product such as Cataclean, or a full fuel system cleaner such as the STP Ultra 5 in 1 Fuel System Cleaner and Stabilizer.

These products are straightforward to use. Pour them into the gas tank while the tank is at the specified fuel level (often around 4 gallons in the tank).

Typically, you want to run the gas tank as close to empty as possible before refilling again to get the most out of the product. Check product instructions for best results.

How To Deep Clean Your Catalytic Converter

cleaning a catalytic converter

No luck with the additives? Don’t worry. You could still try removing and cleaning the catalytic converter the old fashioned way.

1) Remove Catalytic Converter

Unbolt the catalytic converter from the car. There are usually two bolts on the upstream side and two bolts on the downstream side of the exhaust. Some vehicles integrate the catalytic converter into the exhaust manifold. The catalytic converter is a bit harder to remove in these cases.

Remove the downstream O2 sensor(s) if attached to the catalytic converter. You may need a special O2 sensor socket to make this easier.

2) Pressure Wash the Catalytic Converter

Using a pressure washer is a great way to free stubborn debris and build-up. Use a low power setting (around 800 psi) and make sure to keep your hands clear of the spray. Pressure wash through the honeycomb structure.

3) Soak in Soapy Water

Place the catalytic converter in a bucket of hot, soapy water to soak for an hour. This will help free build-up that the pressure washer missed.

4) Rinse and Repeat

Rinse off the catalytic converter with the pressure washer. If you still see debris inside the honeycomb, repeat this process but soak the unit for a longer period of time.

5) Air Dry Completely

Once you’re satisfied with the cleanliness of your catalytic converter, let the unit air dry completely. This may take up to a day or even longer, depending on your local weather. Once the catalytic converter has dried, reinstall the catalytic converter and O2 sensor(s).


Some catalytic converter cleaning products work best as a preventative measure, and won’t offer much help if you have a high mileage cat. In some cases, the only option is to replace the catalytic converter.

If you opt to replace the catalytic converter, be aware that many vehicles are sensitive to aftermarket catalytic converters. Some vehicles will throw codes even with a brand new aftermarket catalytic converter. In this case, you might have to resort to buying the more expensive OEM catalyst.


3 thoughts on “5 Steps to Clear a Clogged Catalytic Converter by Yourself”

  1. lots of people dont know where the catalyst converter is, so this job may not be for everyone, time to call a mechanic…

  2. you have o have an automotive shop or an auto , lift to even TRY to work on a catalytic converter.NO person can do that without it,you may as while have the shop to do it

    • You could do it on a set of jack stands, which are fairly inexpensive. I bought these jack stands for a truck and I am really happy with them.

      These stands have a double locking feature for added safety. If you have a smaller vehicle, you probably won’t need 6 ton stands but they’ll certainly do the job. Just make sure you buy stands that can support the weight you need.


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