5 Steps To Clear A Clogged Catalytic Converter By Yourself

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So you’ve narrowed down the problem to the catalytic converter. But at $900 to $2,500 for replacement, it may be worth trying a much cheaper option first.

If your converter is clogged with carbon deposits rather than physically damaged, cleaning it could solve the problem for under $50 (or even free). Here’s how to determine if yours is cleanable and the methods you can use.

Purpose of a Catalytic Converter

The catalytic converter (or converters since many vehicles have two or more) sits in your exhaust system and reduces harmful emissions before they exit the tailpipe. Inside is a ceramic or metallic honeycomb structure coated with precious metals like platinum, palladium, and rhodium.

As hot exhaust gases pass through this honeycomb, a chemical reaction occurs. The precious metals act as catalysts to convert toxic pollutants (carbon monoxide, unburned hydrocarbons, and nitrogen oxides) into less harmful substances like carbon dioxide (CO₂), water vapor (H₂O), and nitrogen (N₂).

Over time, the honeycomb can become clogged with carbon buildup, oil ash, or coolant residue. When this happens, exhaust gases can’t flow through properly, reducing engine performance and increasing emissions.

Signs Your Catalytic Converter Needs Cleaning

• Check Engine Light – Codes such as P0420 and P0430 indicate that the catalytic converter’s efficiency is below the threshold set by the vehicle’s onboard diagnostics system. While this often points to a failing converter, it can also be triggered by faulty oxygen sensors, exhaust leaks, or engine misfires. A scan tool will reveal these specific codes, but further diagnosis will be needed.
• Reduced Engine Performance – A partially clogged converter restricts exhaust flow, making it harder for the engine to expel gases. You’ll notice sluggish acceleration, reduced power, or even engine hesitation, especially when merging or climbing hills.
• Poor Fuel Economy – Restricted exhaust flow forces the engine to work harder, burning more fuel to produce the same amount of power. If you’ve noticed your fuel economy dropping without other explanation, the catalytic converter could be the culprit.
• Failed Emissions Test – Since the converter’s job is to reduce harmful emissions, a clogged or failing unit will cause your vehicle to fail an emissions test. This is often one of the earliest signs of a problem.
• Sulfur/Rotten Egg Smell – A failing converter may not fully process sulfur compounds in the exhaust, producing a strong rotten egg odor. However, this smell can also result from fuel mixture problems, so it’s not always definitive.
• Rattling Noise from Underneath – If the internal honeycomb structure has broken apart, you’ll hear a rattling sound from under the car when starting or accelerating. This means the converter needs replacement (cleaning won’t help).
• Difficulty Starting – Severe blockage can create so much backpressure that the engine struggles to start or won’t start at all. This is rare but indicates a nearly or fully clogged converter.

When Cleaning Will Work (vs When You Need Replacement)

Cleaning only works if your catalytic converter is clogged by carbon or soot buildup. If the internal honeycomb structure is physically damaged, no amount of cleaning will fix it.

When Cleaning Might Work

Light to moderate carbon buildup from normal driving or extended idling is the ideal candidate for cleaning. If your check engine light just came on recently and you haven’t noticed any rattling noises or severe performance loss, there’s a good chance cleaning could help restore partial efficiency.

Vehicles used mainly for city driving are more prone to this type of buildup.

When You Need Replacement

If you hear rattling from underneath the vehicle, the honeycomb (ceramic substrate) inside has cracked or broken apart (cleaning won’t fix this). A melted or fused substrate (often from running too rich or misfiring cylinders) also requires replacement.

Likewise, converters contaminated by oil burning or coolant leaks typically require a new converter, though you must also fix the root cause or the replacement will fail quickly as well.

See Also: 5 Symptoms of a Bad Catalytic Converter

Checking for Backpressure

You can test for excessive backpressure by removing the upstream oxygen sensor and starting the engine. If the engine runs significantly better with the sensor removed, the converter is likely clogged. A mechanic can confirm this with a backpressure gauge or vacuum test (readings above about 3 psi at 2,500 RPM typically indicate restriction).

Before attempting any cleaning method, try to determine the severity of the clog. If the vehicle barely runs or won’t start at all, the blockage is likely too severe for cleaning to work.

How to Clean Your Catalytic Converter

🏎️ Method #1: Italian Tune-Up

An Italian tune-up is the simplest and cheapest way to clean a catalytic converter because it costs nothing. The concept is straightforward: drive at high RPM on the highway to get the exhaust system hot enough to burn off light carbon or soot deposits.

Take your vehicle on a highway and accelerate hard, keeping the RPMs high (around 3,000-4,000 RPM) for about 15-20 minutes. The sustained high temperature (often reaching over 1,100°F) helps burn away buildup inside the converter. This works best for light deposits caused by short trips or extended idling.

Make sure the engine is already at operating temperature before you start, and only do this if the vehicle is running reasonably well. Don’t attempt this method if the engine is misfiring, burning oil, or running rich, since that can overheat and damage the converter.

This method is hit or miss. If the clog is minor, you might notice improved performance and the check engine light may turn off after a few drive cycles. If nothing changes after trying this a couple times, you’ll need to move on to other methods.

Cost: Free

🧴 Method #2: Catalytic Converter Cleaner Additive

Fuel additives are designed to help clean the catalytic converter from the inside as you drive. Products like Cataclean, OxiCat, and Liqui Moly Catalytic System Cleaner are poured directly into your fuel tank and work their way through the fuel and exhaust systems.

The cleaner mixes with your fuel, passes through the combustion process, and reaches the catalytic converter as part of the exhaust flow. The chemicals help reduce carbon and soot buildup and can improve exhaust flow if the clog is minor. For best results, add the cleaner when your tank is nearly empty, fill up with fresh fuel, and drive normally.

Most products recommend driving 50-150 miles to allow the cleaner to work through the system. Highway driving helps because higher exhaust temperatures make the cleaning process more effective. You may need to repeat the treatment if the first bottle doesn’t fully resolve the issue.

This method works well for moderate carbon buildup but won’t fix physical damage or severe clogs. If you don’t see improvement after a couple treatments, cleaning probably won’t solve your problem and the catalytic converter will need to be replaced.

Cost: $15-$30 per bottle

Related: 10 Best Catalytic Converter Cleaners for Your Car

💧 Method #3: Removing and Soaking the Catalytic Converter

This method requires more work but gives you the best chance of cleaning a moderately clogged converter. You’ll need to remove the converter from the exhaust system, soak it in a cleaning solution, and reinstall it once it’s completely dry.

1. Let the exhaust system cool completely (it can stay hot for hours after driving). Raise the vehicle on jack stands.
2. Spray penetrating oil on the bolts or clamps holding the catalytic converter. Exhaust hardware often rusts solid and needs time to loosen.
3. Remove any oxygen sensors using an oxygen sensor socket. Then unbolt the converter from the exhaust pipes.
4. Plug one end of the converter and fill it with degreaser or catalytic converter cleaning solution. A mix of hot water and dish detergent can also work for light buildup. Let it soak for several hours or overnight
5. Rinse thoroughly with a garden hose from both ends to flush out loosened debris. Avoid using a pressure washer unless it’s on a very low setting, as too much pressure can damage the converter’s ceramic honeycomb.
6. Let the converter dry completely before reinstalling. Any water left inside will turn to steam and could crack the internal structure.
7. Reinstall with new gaskets and tighten everything to proper torque specifications.

This method takes several hours and only makes sense if you’re comfortable working under a vehicle. On some cars, the converter is easy to access; on others, you may need to remove heat shields or additional exhaust components first.

Cost: $50-$100 (cleaning supplies, gaskets, possibly new hardware)

👨‍🔧 Method #4: Professional Cleaning

Some shops offer professional catalytic converter cleaning services using ultrasonic cleaning equipment. These methods use high-frequency sound waves in a cleaning solution to remove carbon and soot buildup from the honeycomb structure without disassembling or damaging it.

The shop will remove your catalytic converter and place it in an ultrasonic cleaning tank. The process usually takes a few hours, and the converter is reinstalled the same day. This method is more thorough than anything you can do at home but still won’t fix physical damage to the internal structure.

Professional cleaning makes sense if you’ve tried additives or an Italian tune-up without success but don’t want to invest in a full replacement yet. It’s also a good option if you’re not comfortable removing the converter yourself.

Not all shops offer this service, so you may need to call around. Some exhaust shops and muffler specialists have the equipment, while others will need to send the converter out to a specialty cleaning facility.

Cost: $150-$400 depending on the shop and your location

Things That Won’t Work (Myths to Avoid)

You’ll find plenty of questionable advice online about cleaning catalytic converters. Here are a few methods to avoid.

Pouring Lacquer Thinner in the Fuel Tank

Some people claim that adding lacquer thinner or acetone to your fuel tank will clean the converter. While these solvents can help dissolve certain residues, they can also damage fuel lines, injectors, and oxygen sensors.

They’re highly flammable and not safe for modern fuel systems. Stick with cleaners specifically designed for catalytic converters and fuel systems.

Using Excessive Additives

More isn’t better when it comes to fuel additives. Using multiple bottles or stronger concentrations than recommended won’t speed up the cleaning process and can cause other issues, like fouled plugs or damaged sensors. Always follow the instructions on the product label.

Trying to Clean a Physically Damaged Converter

If the honeycomb inside is cracked, melted, or broken apart, no cleaning method will fix it. You’re wasting time and money trying to clean a converter that needs replacement. Listen for rattling noises or severe performance loss; both signs of internal damage.

Legal Considerations

Catalytic converters are regulated under federal and state emissions laws, and violating these rules can lead to significant fines.

Removing Your Catalytic Converter is Illegal

Federal law under the Clean Air Act (42 U.S.C. §7522(a)(3)(A)) prohibits removing or disabling any emissions control device installed on a vehicle (which includes the catalytic converter). This applies even if your state doesn’t require emissions testing. The EPA can issue fines of up to $2,500 per violation for individuals, and much higher for repair shops.

Some states impose additional penalties. You also can’t legally remove a converter to “clean” it and then drive the vehicle on public roads without reinstalling it.

Aftermarket Converters Must Be CARB or EPA Compliant

If you need a replacement, aftermarket catalytic converters must meet EPA standards in most states. California, New York, and a few others follow stricter CARB (California Air Resources Board) rules. Installing a non-compliant converter is illegal and can cause your vehicle to fail inspection.

Always verify that any replacement converter is certified for your vehicle’s year, make, model, and emissions classification. Some universal-fit converters are not legal for on-road use in certain states.

Warranty Implications

Tampering with emissions equipment can void your vehicle’s warranty. Federal law also allows manufacturers to deny warranty claims if a failure was caused by improper maintenance, modification, or the use of non-approved parts.

If your car is still under warranty, check with the dealer before attempting any catalytic converter cleaning where it is removed from the vehicle. It’s always best to confirm what’s covered under your emissions warranty before doing anything that might affect it.

If your vehicle is out of the original warranty period and you haven’t purchased an extended warranty, any work you do yourself won’t affect existing coverage. But, it’s still smart to follow proper procedures to avoid future issues.

See Also: What To Do If Your Catalytic Converter Was Stolen

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KevinKevin has been fascinated by anything automotive since his first go-kart as a kid to his time working as an auto tech for Dodge after obtaining his degree in automotive technology. When he's not working on cars or writing about them, you can find him and his E36 M3 at an event with the local chapter of the BMW CCA. Latest posts by Kevin (see all)

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