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8 Bad Catalytic Converter Symptoms You Should Know (+5 FAQs)

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If you notice an illuminated engine light, the smell of sulfur dioxide, or experience weak engine performance while driving, you may have a bad catalytic converter. 

If that isn’t scary enough, your entire engine may start to rattle when your catalytic converter isn’t working properly.

Is that the end of the list?
We’re afraid not.

While your ‘CAT’ is designed to last the lifetime of your vehicle, it’s still subject to damage. So, it’s essential that you identify a bad catalytic converter before things get out of hand. 

This article will go through 8 bad catalytic converter symptoms, so you’ll know if your CAT needs a lookover, and answer some important FAQs, too. 

This Article Contains 

Let’s get started.

8 Bad Catalytic Converter Symptoms 

Catalytic converters are important as they convert toxic gases, like carbon monoxide and nitrogen oxide, into less harmful gas, like carbon dioxide. 

While they aren’t prone to failure, general wear and tear may lead to eventual catalytic converter failure and resultant (and expensive) repairs or replacements down the road! A faulty catalytic converter will also cause your vehicle to fail an emissions test.

No one wants to spend unnecessary money on fixable car parts, right? 
That’s why you need to identify your failing catalytic converter before it’s completely broken. 

Here are a few ways to identify a faulty catalytic converter: 

1. Rotten Egg Smell from the Exhaust

A tell-tale sign of a catalytic converter problem is a rotten egg smell from the exhaust when you drive. 

All gasoline contains sulfur. The catalytic converter processes this smelly sulfur into odorless sulfur that comes from the exhaust system.

When your catalytic converter isn’t operating correctly, this conversion doesn’t occur. Unburnt fuel and exhaust gasses still containing hydrogen sulfide are emitted, resulting in a rotten egg smell. 

2. Illuminated Check Engine Light 

If your catalytic converter isn’t operating as it should, the check engine light on your dashboard will alert you. 

How does this happen? 
Most modern vehicles are built with an oxygen sensor that monitors the efficiency of the catalytic converter. When harmful gasses aren’t appropriately catalyzed, the oxygen sensor will detect high unprocessed exhaust gas levels. This will illuminate the check engine light. 

3. Rattling Noises  

A faulty catalytic converter produces a rattling or knocking sound while driving or idling. 

This happens when the honeycombs inside the converter begin to collapse or break apart from wear and tear. 

4. Frequent Engine Stalling 

The primary purpose of a catalytic converter is to convert toxic gas like carbon monoxide and nitrogen oxide to less harmful emissions so that they can be safely emitted from the exhaust system. 

A clogged converter will restrict harmful gas conversions and emissions and keep them inside the engine. This will cause your car to stall frequently and make starting the vehicle more challenging

5. Weak Acceleration 

If you notice reduced engine performance and power in your vehicle, especially when driving up steep inclines, there may be a catalytic converter problem. 

If other engine parts like the spark plug, filters, and sensors are still in working condition, then your catalytic converter is the likely culprit of weak acceleration. 

6. Black Smoke from the Exhaust Pipe

You now know that a clogged catalytic converter prevents gasses from exiting the engine properly. As these harmful gasses build up, they become thicker and darker. 

Thick, dark-colored emissions from your exhaust pipe may indicate that you have a clogged or damaged catalytic converter.

7. Engine Misfire 

Another of the clogged catalytic converter symptoms is misfiring, because the clogging restricts oxygen flow within the engine. 

Engines require a lot of oxygen to combust fuel properly. When there isn’t enough oxygen, an excessive amount of unburnt fuel or gasses containing hydrogen sulfide will collect in the cars engine leading to limited exhaust flow. This can cause a recurring engine misfire while you drive.

8. Reduced Fuel Economy

Reduced gas mileage is one of the most common clogged catalytic converter symptoms. When the catalytic converter is clogged, the exhaust gas gets trapped inside the engine. 

This leads to improper combustion of fuel, which will make your cars engine much less efficient. It also means that your engine needs to work harder for the same amount of power.

Don’t want to experience bad gas mileage? 
Visit a mechanic for a catalytic converter repair and fix your exhaust flow! 

Now that you have a better idea of the bad catalytic converter symptoms, let’s cover some frequently asked questions. 

5 FAQs About Bad Catalytic Converters 

Here are a couple of answers to important questions about bad catalytic converters: 

1. Can I Still Drive with a Bad Catalytic Converter?

Generally, a damaged or clogged converter won’t affect the driveability of your car. However, it’ll significantly affect your car’s performance. 

Worst-case scenario?
Complete catalytic converter failure means that you may not be able to drive your vehicle at all. When this happens, it’s best to hire a professional mechanic to diagnose and fix the issue. 

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

An average catalytic converter will last for around 10 years or 100 000 miles if properly looked after. 

The quality of the component, the type of vehicle, and the regularity of vehicle maintenance can all affect the lifespan of the catalytic converter. 

3. How Can I Unclog My Catalytic Converter?

An effective way to unclog your catalytic converter is by using an engine-cleaning liquid or thinner. 

The catalytic converter is found between your muffler and the exhaust manifold.
Ensure that your car has over 15 liters of fuel, and then pour the engine cleaner into the fuel tank. Drive your car for around 30 minutes until the fuel runs out. 

You’ll know if the process has been successful if you no longer experience engine performance issues and your vehicle passes an emissions test. 

However, if you don’t feel comfortable unclogging the catalytic converter, contact a mechanic for help. 

4. What Diagnostic Codes Mean a Catalytic Converter Issue?

You can use an OBD Scanner to diagnose engine issues, from spark plug problems to piston issues. 

The following error codes indicate that you have a failing catalytic converter: 

5. How Much Does a Catalytic Converter Replacement Cost?

Replacing a catalytic converter tends to be very expensive. This is because catalytic converters contain precious metals like small amounts of platinum, rhodium, and palladium. The same precious metals also make catalytic converters more prone to theft than other car parts.

Catalytic converter replacements can cost anywhere between $400 – $2500, excluding labor. 

Expensive right?
It’s smart to visit a mechanic regularly for catalytic converter repair and maintenance to avoid paying large sums of money in the future. 

Final Words 

A damaged catalytic converter results in a wide range of symptoms, from harmful emissions to reduced engine performance, reduced fuel economy, and increased emissions. 

When you notice one of these symptoms, it’s best to contact a professional to diagnose and repair the issue. 

But who do you contact when you have catalytic converter trouble?
RepairSmith

RepairSmith is an accessible mobile auto repair service that you can contact seven days a week. 

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Get in touch soon to ensure that your vehicle is in tip-top shape!