Auto Parts - How to Clean a Catalytic Converter and Why - New - Blog

You likely don’t think about your catalytic converter too often. But the moment the check engine light flicks on, acceleration feels sluggish, or there’s a rotten egg smell coming from your exhaust, it might be time to investigate your catalytic converter’s condition.

These are all symptoms of carbon buildup. The good news is, addressing it early and cleaning your catalytic converter can save you from a replacement job.

What Is a Catalytic Converter and What Does It Do?

The catalytic converter is a key part of your exhaust system. Sitting between the engine and the tailpipe, it contains a ceramic honeycomb structure coated with platinum, palladium, and rhodium. These precious metals trigger chemical reactions that convert CO, hydrocarbons, and NOx into CO2, water vapour, and nitrogen — removing roughly 90% of harmful emissions from your exhaust.

Under the Canadian Environmental Protection Act, all vehicles originally equipped with a catalytic converter must keep a functioning one to stay street-legal in Canada.

What Causes a Catalytic Converter to Get Dirty?

Many factors can lead to carbon buildup and contamination within your catalytic converter:

• Frequent short trips that prevent the converter from reaching operating temperatures (especially common in Canadian winters, when engines take longer to warm up). The converter needs to reach roughly 400°C to trigger the chemical reactions that burn off deposits. Short trips often don’t give it enough time to get there.
• Engine misfires that push unburned fuel into the exhaust.
• Engine that runs rich due to a faulty O2 sensor, bad fuel injectors, or worn spark plugs. When the fuel mixture is off, excess unburned fuel enters the exhaust stream and coats the converter’s honeycomb structure, restricting flow over time.
• Low-quality fuel. For example, fuel with high levels of sulphur reduces the converter's efficiency by coating the catalyst. Low-quality fuel can also encourage residue buildup.
• Oil or coolant leaks entering the exhaust system. Unlike carbon buildup from normal combustion, contamination from oil or coolant can permanently damage the catalyst, making cleaning ineffective and replacement the only option.

Signs Your Catalytic Converter May Be Clogged

Many common symptoms of carbon buildup in the converter can overlap with other exhaust or engine issues, so it’s worth ruling out other causes before assuming the converter is the problem. If you’re seeing more than one of these symptoms at the same time, the converter is a strong candidate:

• Reduced power and sluggish acceleration, especially when travelling uphill.
• Rotten egg or sulphur smell from the exhaust.
• Check engine light, specifically OBD codes P0420 or P0430. These codes indicate the converter isn’t reducing emissions efficiently enough for the vehicle’s sensors, and they’re one of the clearest diagnostic signals available to a DIYer with an OBD scanner.
• Poor fuel economy.
• Excessive heat under the vehicle.

If you notice a rattling sound from under the vehicle while the car is running, this is a sign the converter’s internal substrate has physically broken apart — cleaning won’t help.

How to Clean a Catalytic Converter Without Removing It

There are two methods to effectively clean your catalytic converter.

Method 1—Fuel Additive

This is the simplest and lowest risk approach to cleaning your converter.

Add a bottle of catalytic converter cleaner to a roughly half-full fuel tank in sedans and a quarter full tank in trucks and large SUVs, then drive at a normal speed for 30 to 60 km, allowing it to circulate through the engine and exhaust.

The cleaner helps dissolve light carbon deposits as the engine runs. Rislone Cat Complete (RLN 34720) is an effective catalytic converter cleaner and is safe for O2 sensors.

Method 2 – Extended Highway Driving

Only attempt this method if your engine is otherwise in good health. For example, cleaning your catalytic converter using this method with an active misfire issue can cause the converter to overheat.

Drive at sustained highway speeds with higher RPMs above 3,000 for 20 to 30 minutes to help raise exhaust temperatures to passively burn off light deposits.

Method 1 should be your first step as a DIY method to clean your catalytic converter. Method 2 should be a complementary follow-up.

If you’re experiencing misfires or warning lights, it’s best to address these issues first before attempting either cleaning method.

What About Manual Cleaning (Removing the Catalytic Converter)?

If adding fuel additives didn’t resolve your converter issues, the next step is a professional assessment. Do not attempt an off-vehicle converter clean on your own. You run the risk of damaging the ceramic substrate.

When Cleaning Doesn’t Work—and What to Do Instead

Cleaning only works if your carbon buildup is mild. If any of the below issues exist, a converter cleaning won’t resolve your problem:

• The ceramic honeycomb has melted or broken apart and is causing a rattling sound.
• The converter glowed red-hot from a severe misfire event.
• Oil or coolant contamination has poisoned the catalyst.
• The P0420/P0430 code keeps returning after being cleared.

In these cases, a converter replacement by a trained mechanic is the only fix. A NAPA AUTOPRO technician can also address whatever caused the failure, like misfires, oil leaks, or bad sensors, before installing a new converter to avoid another failure.

How to Prevent Catalytic Converter Buildup

These preventative habits can extend the life of your converter:

• Take the car on a longer highway drive occasionally, especially if most trips are short.
• Address warning lights and engine misfires as soon as possible.
• Use high-quality fuel.
• Keep up with routine vehicle maintenance, like replacing spark plugs, O2 sensors, and oil changes.

Prompt response to any issues and proactive vehicle maintenance can extend the life of your vehicle and critical parts. For projects requiring specialized skills and tools, find your local NAPA AUTOPRO for expert maintenance support.

Catalytic converter cleaning only works when you catch carbon buildup early. A fuel additive is the most accessible tool a DIYer has at their disposal, but knowing when to stop troubleshooting and replace the converter is just as important.

For the best advice, visit your local NAPA Auto Parts store to speak with an automotive expert or browse our full selection of exhaust system essentials at www.NAPACanada.com.