What are the Symptoms of a Clogged Catalytic Converter?

Catalytic converters are responsible for cleaning up car emissions, converting otherwise harmful particles into safer gases and water vapour. But what happens when they become clogged or develop faults?

Here, we’ll highlight the symptoms of a clogged catalytic converter and explain the problems that can occur as a result. It’s also worth outlining how catalytic converters work so that you can understand why these types of problems happen and the best ways to resolve them.

Use the links below to navigate or read on below for the full guide.

• How do catalytic converters work?
• What are the symptoms of a clogged catalytic converter?
• What problems can a blocked catalytic converter cause?
• Can you clean a catalytic converter?

How do catalytic converters work?

Catalytic converters sit in the exhaust system, where they collect harmful gases like carbon monoxide and hydrocarbons, converting them into carbon dioxide and water that is released from the tailpipe.

Converters contain ceramic “pores” coated with a mix of palladium, rhodium, and platinum. When this coating is exposed to hot engine emissions, it heats up, changing the chemical structure of the pores. This, in turn, acts as a barrier, removing harmful gases and converting particles into nitrogen and oxygen.

The below diagram offers a simple demonstration of how catalytic converters work…

The result is impressive. Catalytic converters are capable of removing a substantial number of harmful particles from exhaust gases, limiting the volume of hazardous fumes escaping through the tailpipe.

What’s more, catalytic converters are highly durable and require minimal maintenance to keep them working at their best. Still, checks and servicing at regular intervals can help to ensure that a converter is working as it should.

What are the symptoms of a clogged catalytic converter?

While catalytic converters are a durable and well-considered solution, they can develop problems that you need to be aware of. There are a few symptoms that can tell you there’s an issue with your car’s catalytic converter, including:

Sluggish engine performance and poor acceleration

If you’ve noticed a drop in how your car is performing, this is a tell-tale sign of trouble with the catalytic converter. The engine might sound rough and choked at idle, you may experience more stalls than usual, and the accelerator pedal may not respond as usual.

Heat from under the car

Have you noticed heat billowing out from beneath your car? You’re not going mad – it’s probably resonating from the converter.

When the converter becomes clogged, hot exhaust fumes build within the pores of the unit. You might be able to feel this heat outside and inside your car, and it’s definitely a symptom you won’t want to ignore for long.

Rotten egg smell

Don’t dismiss that smell wafting into your car as a nearby farm because it could be coming from your car’s catalytic converter.

When there’s a problem with the system, sulphur particles aren’t dispersed as they should be. This can produce a smell like rotten eggs that you might notice when driving.

Dark exhaust fumes

 If the fumes coming from your car’s exhaust are dark, this is a key indicator of converter issues. When they’re working properly, converters break down carbon and other harmful particles; if the fumes are dark, it means they’re still there.

Get your car checked as soon as possible if you notice dark smoke coming from the exhaust. Not only could this mitigate expensive repair costs, but it will also ensure you’re keeping day-to-day emissions to a minimum. Plus, high emissions could also result in MOT failure.

What problems can a blocked catalytic converter cause?

We’ve covered the symptoms of a clogged catalytic converter, but what broader issues can this cause?

Most of the problems associated with blocked converters stem from heat damage. If a unit is blocked, the fumes inside reach extremely high temperatures, which can result in damage to the special coating lining each of the catalytic pores. This means fewer harmful particles are treated and transformed, which is when symptoms start appearing.

If the problem goes untreated, heat can melt the converter from the inside out, leading to a significant repair bill. It may be possible to clean and “patch” the unit if the damage is only minor, but a replacement may be needed in the worst cases.

Elsewhere, a failing catalytic converter can interrupt a vehicle’s ECU and oxygen sensor, which is why engine problems are a common symptom. The catalytic convert, ECU and oxygen sensor work together to limit poisonous fumes from the exhaust, so when there’s a problem with either of these components, you’re likely to encounter efficiency and performance issues.

Can you clean a catalytic converter?

There’s no approved, go-to process for cleaning a catalytic converter, though there are some additives that claim to do the job. In general, though, you’ll never need to clean your car’s catalytic converter if you keep on top of maintenance and servicing.

Sticking to the manufacturer’s approved service schedule can help to keep the catalytic converter working as it should. That should include an air filter change or clear out, as well as the customary oil change and coolant checks.

Another effective way to safeguard your catalytic converter is by using fuel additives. Petrol and diesel fuel additives maximise engine efficiency to ensure that fuel is being burned as efficiently as possible. This limits the number of carbon particles entering the exhaust, so the catalytic converter doesn’t need to work as hard and is less likely to become blocked.

Has this guide to clogged catalytic converters been useful? Get more help and advice over the Redex blog. Looking for fuel additives that deliver a better drive? Explore our full product range or get in touch with our experts for information.