Tips and Advice

What is a catalytic converter?

All new cars have a catalytic converter, but what exactly is it? Carbuyer explains

Catalytic converters, or ‘cats’, were introduced in 1975 as a way of reducing the amount of pollution in exhaust fumes. They have been a legal requirement on all new petrol and diesel cars since 1993. Most new cars also feature a particulate filter in order to meet the latest Euro 6 emissions standards.

What does a catalytic converter do?

A catalytic converter turns some of the engine’s harmful pollutants into carbon dioxide and water vapour. A metal exterior hides a delicate honeycomb structure that’s coated in precious metals such as palladium, rhodium and platinum. When heated, these materials cause a chemical reaction that purifies the exhaust gases. Because they need to be hot to work best, catalytic converters are usually placed near the engine where the temperature is highest.

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How long does a catalytic converter last?

You can expect a cat to last for at least 10 years, with many continuing to work until the end of the car’s life. However, they can fail prematurely in certain circumstances, which can lead to a very hefty bill. If you only make short journeys, where the engine hasn’t had a chance to warm up properly, the cat may not work as it should and may need replacing before the car’s a decade old.

What happens when a catalytic converter goes wrong?

Many newer cars will have inbuilt software that can detect when the catalytic converter has failed, but you’ll be able to tell if something’s wrong with it. If you notice that your car isn’t performing as well as normal, or that there’s dark smoke coming out of the exhaust, it could be a sign that your catalytic converter isn’t working correctly. Other telltale signs include a sulphuric, rotten egg-like smell from the exhaust and lots of heat coming from the underside of the car.

The different types of exhaust smoke you should look out for

A cat malfunction can be caused by a number of things. If you only do very short journeys, it may become clogged up with carbon deposits, while fluids like oil and coolant can also affect it. If there’s anything wrong with the air flow to the catalytic converter, like a faulty lambda sensor or the exhaust gases not getting through, this can damage it too. Some catalytic converters can be susceptible to potentially damaging scrapes and bangs because they’re mounted on the underneath of the car.

MOT tests will check your car’s emissions, and the car will fail if it exceeds a set level. So while it’s not illegal to drive without a catalytic converter, it’s very unlikely your car will pass if you don’t have one, or if it’s not working.

Is it worth using a catalytic converter cleaner?

You can clean your catalytic converter either by taking the car to a garage and letting a mechanic do it or by using a fuel system cleaner, which is meant to destroy any soot or carbon particles. If you drive on a motorway or dual carriageway on a fairly regular basis, your cat shouldn’t need cleaning very often, if at all. However, as we’ve mentioned above, many short journeys can reduce a cat’s lifespan, but occasionally cleaning it should substantially prolong its usefulness.

Catalytic converter cleaners tend to be between £5 and £20 for a bottle, and you simply pour it into your fuel tank like petrol or diesel. You won’t need to use it very often, and it’s certainly cheaper than a the cost of a new one - you’ll be looking at a bill of hundreds, if not thousands, of pounds if you need to replace your catalytic converter.

Catalytic converter theft

Unfortunately, cats can be an easy target for criminals, as the precious metals inside can be very valuable. To prevent yours being stolen, you can have the serial number etched on to it to make it harder to sell, install CCTV cameras overlooking your car, weld the bolts shut or install a protective case, although the latter can be an expensive option.

Some cars now have the catalytic converter built into the engine’s manifold, making it much harder for thieves to steal.

Read our guide to diesel particulate filters (DPFs), which also help reduce emissions produced by diesel engines, while our dashboard light and amber warning light guides will help you understand what’s gone wrong with your car.

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