Top 10 Symptoms of a Clogged Catalytic Converter

Symptoms of Clogged Catalytic Converter

Signs of a clogged catalytic converter include a sulfurous odor from the exhaust, an overheated engine, or a decrease in power.

Let's go through some other signs and what to do if you suspect your catalytic converter may be clogged.

Symptoms of a Clogged Catalytic Converter

1. Loss of Engine Power

If you notice that your engine doesn’t release enough power when you hit the pedals, there are chances that you have a clogged catalytic.

When your catalytic converter clogs, exhaust gasses will get stored in your vehicle’s system. This will increase exhaust pressure which will, in turn, reduce the performance of your engine.

A clogged catalytic converter will cause a loss of engine power when you are trying to accelerate or climb a hill. Here’s how a clogged catalytic converter causes loss of engine power.

Most cars with diesel and gas engines use the otto 4-cycle engine operation. One of the otto 4-cycle engine operations entails that the engine generates/consumes power with the exhaust stroke. This process involves the pushing out of gasses through the exhaust system after each power stroke.

Forcing out the gasses of the exhaust system consumes some power generated through the process of burning fuel. The restriction of these gasses makes the engine require more power to function.

This will cause your car to use too much power to push out the gasses from the exhaust system, which leaves little or no power to drive the car.

2. Smell of Sulfur

The smell of Sulphur is a good indicator that you have a clogged catalytic converter. A clogged catalytic converter smells like sulfur or rotten eggs.

This is because a clogged catalytic converter causes the exhaust system to release harmful pollutants that weren’t converted.

Sulfur gas is one of the harmful gasses emitted from the system. Naturally, your car produces toxic gasses like hydrogen sulfide after each combustion process. It is the work of the catalytic converter to make these gasses less harmful before they are released from the tailpipe.

When the catalytic converter is bad or clogged, these gasses are released but with airflow restriction. If you notice some unpleasant smell coming from your tailpipe, you should check your catalytic converter.

3. Overheating Engine

A clogged catalytic converter prevents the free flow of exhaust emissions out of your car’s system. This ends up increasing the buildup of pressure and heat in your car’s engine.

The exhaust manifold overheats when the hot exhaust fumes cannot move out freely. This impacts the temperature of your engine.

The overheating engine will result in a burning smell under your car. This is because your exhaust manifolds are roasting. You can easily perceive the smell or should look out for an increased release of exhaust fumes.

4. “Check Engine Light” Comes On

In some cases, a clogged catalytic converter will trigger a “check engine light” indicator on your car’s dashboard. Some cars will send a P0420 fault code on your dashboard.

A P0420 error code might not specifically indicate that your catalytic converter is clogged, but it sends a signal that something is wrong with your catalyst system. This can call for a change of your engine coolant temperature sensor, a check for exhaust pipe leaks, or the replacement of the exhaust manifold.

In common cases, the check engine light and the P0420 error code indicate that you need to change your catalytic converter.

5. Poor Fuel Economy

Poor fuel economy and reduced gas mileage are strong indicators that you have a clogged catalytic converter. There are, however, disputes surrounding the relationship between fuel economy and clogged catalytic converters.

A lot of drivers argue that clogged catalytic converters have nothing to do with your fuel economy.

This is slightly true because the catalytic converter handles the burning up of reactive exhaust gasses and has no direct contact with the fuel hose.

But when your catalytic converter is clogged, your engine has to work harder to keep up with the power that your car needs to function. This is because a greater amount of power is burned in the exhaust system.

However, a clogged catalytic converter might not largely influence your fuel economy, but reduced fuel efficiency is a symptom to look out for.

6. Sluggish Rides

With your vehicle battling with low power because of the failing catalytic converter, you will experience sluggish rides.

You will experience reduced acceleration, low power, and poor driving performance. This will always turn out to be a dangerous experience if you are playing on the road with it.

You will find it hard to overtake vehicles, and no matter how hard you hit the gas pedals, the power delivery wouldn’t meet up needs.

If you notice a reduction in your driving performance, with frequent occurrence of sluggish rides, you should check your catalytic converter.

7. Increased Exhaust Pressure in the Tailpipe

Clogged catalytic converters generate excessive back pressure in your exhaust. Increased back pressure can cause an imbalance in the air-fuel mixture. This can cause your engine to stall or influence overheating and reduce your engine power.

A clogged catalytic converter affects your exhausts' breathability. This can go as far as causing vibrations in your car or a wild burst of pressure on your engine.

8. Rattling Noise

Rattling noise is one of the symptoms of a clogged catalytic converter. This is a general symptom of bad catalytic converters. The more your catalytic converter remains clogged, the more noise they tend to make.

This noise happens because the ceramic honeycombs of your “CAT” have started to fall off. The rattling noise will increase as you try to accelerate the car.

9. Engine Misfires

Clogged catalytic converters restrict the free flow of fumes in the exhaust system, this traps exhaust gasses in the combustion chamber.

When this happens, the engine ignites, and compressed exhaust gasses mix with the air-fuel mixture. The improper mixture creates an imbalance in your engine that will cause a misfire.

In extreme cases where the gasses can’t go out, they go back to your intake manifold, and this will cause the engine to fail. Your engine will start, and after a few seconds, it will go off.

10. Engine Won’t Run

In rare cases, a clogged catalytic converter can prevent your engine from running. In this case, the engine ignites even when the intake manifold is closed. Your engine won’t run until there is a passage creation for the release of gasses.

Your car’s engine will only fail to run because a failed catalytic converter is completely blocked. This will happen because of neglecting the symptoms at an initial stage.

What Causes Catalytic Converters To Get Clogged?

Catalytic converters are usually clogged by carbon deposits and poor maintenance. These catalytic converters will get clogged when air and oil find their way into the exhaust system.

This will cause a build-up of carbon and soot, which will clog the converters and the air passage in your exhaust system. This usually clogs the surfaces of the ceramic honeycomb preventing proper ventilation and air passage in the system.

Clogging of the catalytic converters can be largely avoided when you carry out routine maintenance on the vehicle.

What Problems Can A Clogged Catalytic Converter Cause?

Here are common problems that a clogged catalytic converter will cause:

  • Sluggish rides.
  • Poor engine performance.
  • Engine shutdown.
  • Reduced fuel efficiency and gas mileage.
  • Reduced acceleration.
  • Excessive buildup of heat under your car.
  • Overheating.

What Could Damage A Catalytic Converter?

Here are three leading factors that cause damage to a catalytic converter.

1. Overheating

Overheating remains the leading cause of catalytic converter damage. The catalytic converter can get so heated up that the ceramic catalyst starts melting down.

Certain factors can cause the catalytic converter to overheat. Some of these factors include:

  • Bad Oxygen Sensors: Bad oxygen sensors or engine management systems can send bad air-fuel mixture signals, causing the engine to run on too-rich or too-lean mixtures. This will generate too much heat in the catalytic converter, more heat than it can handle.
  • Misfires: Misfires will load the catalytic converter with too much fuel, causing it to overheat.
  • Bad Spark Plugs: Spark plug failures affect the CAT in similar ways as bad oxygen sensors. The too-rich mixture will get into the exhaust, causing a buildup of excess heat. These factors directly or indirectly influence the level of hydrocarbons and carbon monoxide that enters the catalytic converter. This increases the temperature in the converter.

2. Contamination

Lots of contaminants can ruin the catalytic converter. These contaminants include engine oil, internal coolant leaks, or carbon deposits. These contaminants will coat the surfaces of the CAT, preventing the system from breathing properly.

They block the tiny passages and render the catalytic converter useless. In some cases, improper fuel additives can coat the catalytic converter.

3. Physical Damage

Catalytic converters should last up to 10 years and sometimes for a lifetime. This lifespan is usually short-lived when they are physically damaged. There are a lot of things that can physically damage a catalytic converter. They include:

  • Road debris and impacts.
  • Corrosion.
  • Metal fails.
  • Thermal shock.
  • Speed bumps.
  • Intense driving conditions.


Clogged catalytic converters can lead to a lot of problems in your vehicle. You must understand the symptoms and fix them before the issue escalates.

You should run a proper catalytic diagnostic whenever you notice any of these symptoms. This will save you the cost of having to repair the entire exhaust system when you can just replace the bad catalytic converter.

Frequently Asked Questions

Can I unclog my catalytic converter?

Yes, you can. You can unclog your catalytic converter by cleaning it with CAT cleaners and fuel. Some drivers prefer a bottle of water with other CAT cleaners. You must confirm the extent of the clog to verify if unclogging or replacing is the best option.

Can a catalytic converter unclog itself?

No. A catalytic converter cannot unclog itself. You need to play your part in cleaning a catalytic converter. You will need to drop some CAT cleaners into your fuel tank and drive between 4,000 to 6,000 RPMs. You will have to ride at these levels for up to 30 mins.

Does Premium gas clean catalytic converters?

No. Premium gas does not clean a catalytic converter. Premium gas is good for catalytic converters, but there are no indicators that they clean the converters. Premium gas will simply give you a higher-octane formula that allows optimal heat transfer and improved life for your catalysts.

Can you clean a catalytic converter instead of replacing it?

Yes, you can. A lot of car manufacturers will advise against cleaning a catalytic converter instead of replacing it. The risks are valid, and this is because you might end up damaging the catalytic converter while trying to clean it.