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Car Care Advice

7 Symptoms of a Clogged Catalytic Converter (+How to Diagnose)

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If you notice that your engine light is illuminated and you have weak engine power, or you smell rotten eggs while driving, you may have a clogged catalytic converter. 

A few more catalytic converter symptoms could point to this issue.

But how do you diagnose a faulty catalytic converter and know for sure? 

Don’t worry, we’re here to help. 
In this article, we’ll cover the common clogged catalytic converter symptoms, and how to diagnose this problem. We’ll also answer some related FAQs

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Let’s get started!

7 Signs of a Clogged Catalytic Converter 

A large amount of toxic emissions pass through the catalytic converters (CATs), which can eventually end up clogging them. 

When that happens, a clogged catalytic converter will fail to convert these exhaust fumes properly, causing them to get trapped in the combustion chamber and weaken your engine power. This issue needs prompt identification, otherwise your engine could die out completely. 

Here are a few failing catalytic converter symptoms:

1. Illuminated Check Engine Light 

The most apparent of the clogged catalytic converter symptoms is an illuminated check engine light. 

If you notice that your check engine light is on, you can use an OBD scanner to determine whether the catalytic converter is the cause. 

2. Trouble Starting the Car

When a catalytic converter is clogged, it causes a large amount of smoke to surge through the exhaust system. This may lead to frequent stalling or make the car difficult to start at all. 

If the CAT system has a major blockage, your engine will likely sputter and only start a few seconds later. 

3. Poor Acceleration 

Reduced engine performance is one of the most telling signs that your catalytic converter may be clogged. When you notice your vehicle jerking, stalling, and struggling to climb steep hills, it’s likely because of improper combustion.

Why does that happen?
A failing catalytic converter prevents exhaust gasses from flowing through the converter and out of the exhaust pipe. 

At first, you may suspect low fuel pressure. In reality, harmful gasses get stuck in the combustion chamber, leading to incomplete combustion, decreased acceleration, engine performance, and increased engine lag. 

4. Smell of Sulfur and Rotten Eggs

A properly working catalytic converter processes harmful gas into a less harmful emission.

How? 
When gasoline reaches a working catalytic converter, it transforms emissions like hydrogen sulfide into odorless sulfur dioxide. A clogged catalytic converter can’t properly process the sulfur exhaust gasses, which will cause a rotten egg smell

5. Engine Misfires

As the catalytic converter gets clogged, toxic gas trapped in the engine heats up to the point of ignition. 

This ignition makes the engine misfire, damaging crucial engine components over time. If you notice your engine misfire, it’s best to contact a professional ASAP.

6. Poor Fuel Economy 

When your vehicle has a significant blockage in the catalytic converter, your fuel economy and gas mileage will suffer. 

A clogged catalytic converter can cause more exhaust to build up in the engine, reducing the amount of new, combustible oxygen required for proper functioning.

When the engine receives less oxygen, it must work harder to achieve speed. This increased load not only lowers your fuel economy (gas mileage) but also worsens the clog in the converter. 

7. Failed Vehicle Emission Test

Most states require annual vehicle emission tests by car owners. A catalytic converter is the main component responsible for healthy exhaust gas emissions. 

So, your vehicle will most likely fail an emissions test when your catalytic converter is clogged and doesn’t process harmful gasses like carbon monoxide properly. 

Now you understand all of the significant symptoms. 
Once you notice one or more of these signs, you may want to diagnose the catalytic converter problem.

Let’s find out how to do that. 

How to Diagnose a Clogged Catalytic Converter (3 Methods)

There are three ways to diagnose a faulty catalytic converter:

1. Vacuum Test 

Before conducting this test, you’ll need a vacuum gauge. 
Follow these steps to conduct a vacuum test:

2. Temperature Test

To perform a temperature test, you’ll need any type of thermometer, like an infrared or kitchen thermometer. 

3. Back Pressure Test 

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

All three of these tests require some knowledge of the vehicle’s engine. Contact a mechanic if you don’t feel comfortable performing the diagnosis yourself. 

Note: Try out a catalytic converter cleaner to unclog the component. A catalytic converter cleaner can also clean an oxygen sensor or spark plug. You can use this to clean out any carbon deposit. 

Now it’s time to go through a few frequently asked questions. 

3 FAQs about Clogged Catalytic Converters 

Here are the answers to commonly asked questions about catalytic converters:

1. How does a Catalytic Converter get Clogged? 

As exhaust gases, like nitrous oxide and carbon monoxide, pass over the honeycombed catalytic converter, they are processed into a less harmful emission, like carbon dioxide. These are then released from the exhaust system of the vehicle. 

There are three reasons the catalytic converter can get clogged when performing this job: 

Excess unburnt fuel and harmful toxins will allow for a carbon deposit to form in the engine, which can lead to further blockages.

2. What is the Average Lifespan of the Catalytic Converter?

The average lifespan before complete catalytic converter failure is around 100,000 miles, or 10 years (depending on how often you drive). 

Regular vehicle maintenance and engine check-ups can extend the lifespan of your catalytic converter and other engine components in general. 

3. Can a Clogged Converter Cause an Engine to Overheat?

Yes, a bad catalytic converter can cause your engine to overheat. This happens because a clogged converter restricts the exhaust flow and stops hot exhaust fumes from exiting the engine. 

A major blockage will heat up the exhaust manifold, cause catalytic converter failure, and raise engine temperatures, which can wreak havoc on the other engine components.

Note: The exhaust manifold is responsible for gathering up harmful gas and leading them to the catalytic converter.

This is why you need to contact a professional for a catalytic converter replacement or repair. 

Wrapping Up

A bad catalytic converter can lead to many other problems within the engine, including overheating. To prevent further damage, you must pay attention to the faulty converter signs mentioned above. 

If you notice any catalytic converter problem, it’s best to contact a professional.

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