What Is a Catalytic Converter?
Ellie Dyer-Brown, 13 days ago
3 min read
- Exhaust
- How it works
FixMyCar explains everything you need to know about catalytic converters.
Catalytic converters (or simply ‘cats’) often feature in the news alongside panicked headlines about theft. If you’ve ever wondered what they are, how they work and why people steal them, this guide is for you. It contains all the information you need about this crucial part of the exhaust system.
Contents
What is a catalytic converter?
Where would you find a catalytic converter?
Common catalytic converter problems
Symptoms of a faulty catalytic converter
Can you drive without a catalytic converter?
How to clean a catalytic converter
Why do catalytic converters get stolen?
What is a catalytic converter?
Catalytic converters use catalyst substances to transform harmful emissions before they leave the exhaust pipe, including:
Hydrocarbons
Nitrogen oxides
Carbon monoxide
They look similar to exhaust silencers but smaller and contain two ceramic blocks made of thousands of microcellular channels resembling a honeycomb.
The surfaces of these blocks are coated with precious metals like palladium, platinum and rhodium. When exhaust fumes are blown over them, they chemically react - a process aided by heat from the engine - changing toxic gases into carbon dioxide and water vapour.
Where would you find a catalytic converter?
A catalytic converter is part of the exhaust system. You can find it near the exhaust manifold close to the engine, which allows it to warm up quickly, speeding up the chemical reactions within.
Unfortunately, because the catalytic converter is accessible from underneath the car, thieves can slide underneath and use a reciprocating saw to cut it out and sell it.
Common catalytic converter problems
Here are all the things that can go wrong with a catalytic converter.
1. Overheating
The job of a catalytic converter is to convert pollutants into harmless gases. But if too much unburnt fuel enters the cat, it can overheat, causing the inside to melt. The same thing can happen if you have a clogged exhaust silencer.
2. Physical damage
The cat is on the underside of a car, approximately underneath the front seats. This position makes it vulnerable to damage if you drive over debris or a kerb, and you may only notice once the car is lifted on a ramp. That’s why it’s crucial to familiarise yourself with the symptoms of cat failure.
3. Contamination
As well as causing overheating, excessive unburnt fuel can contaminate the catalytic converter, making it fail. Leaking oil and coolant have the same effect.
Several things, such as a clogged oxygen sensor, can cause unburnt fuel to enter the exhaust system. When this happens, your engine may also misfire.
Find out other reasons why your car might be misfiring here.
Fortunately, most issues that can cause contamination are flagged by the appearance of the engine management light on your dashboard. As long as you respond quickly and have your car checked by a mechanic, you may be able to save your cat from damage.
4. Age
The final problem is age. Although catalytic converters last a long time, they don’t last forever, and there’s nothing you can do to prevent them from wearing out. The only thing to do in this situation is book a replacement.
Symptoms of a faulty catalytic converter
If you notice any of the following symptoms, your catalytic converter might be on its way out.
Extreme heat from beneath the vehicle
Learn more about the symptoms of catalytic converter failure in this guide.
Can you drive without a catalytic converter?
You may not notice if your cat has been stolen because it won’t affect your vehicle's performance, so yes, technically, you can drive without one. But that doesn’t mean you should, nor that you’re allowed.
The emissions from your car are considerably higher without a functioning cat - high enough to fail an emissions test. Driving a vehicle on the road without a catalytic converter is illegal due to the amount of toxic gases it produces.
There is another factor to consider: your health. One of the exhaust gases produced by cars without a cat is carbon monoxide, an extremely hazardous gas that sometimes kills people. Driving around without a cat could lead you to breathe in toxic fumes, so it’s best to book a catalytic converter replacement as soon as possible.
How to clean a catalytic converter
The best way to clean your cat is to put an additive in the fuel tank. You can purchase fluids that clean the catalytic converter when they pass through the system.
However, it’s crucial to note that cleaning is a preventative measure that helps prevent clogs; if your cat develops a major clog, you should replace it.
Why do catalytic converters get stolen?
Catalytic converters contain several expensive and rare metals, giving them a high scrap value. Since they are also reasonably easy to access and remove with the right know-how, thieves see this as an opportunity to make money.
Hybrid cars are particularly at risk because their cats tend to be in much better condition than a traditional petrol car with similar mileage.
Check out our ultimate guide to hybrid cars.
How to prevent catalytic converter theft
Here are six tips to avoid cat theft.
1. Buy a catalytic converter clamp or cage
There are a variety of handy devices on the market that cover the catalytic converter and lock it to the chassis, preventing someone from stealing it. Unfortunately, this isn’t a cheap option, costing around £200 for a cage, but it is still cheaper than buying and fitting a new cat.
2. Park off the road or in a well-lit place
Not all drivers have the luxury of off-road parking, but a driveway spot is ideal because it’s much harder for thieves to go unnoticed. Finding a well-lit space is another good deterrent, even if you can’t park your car off the street.
3. Park close to fences or kerbs
The aim of the game is to make it as difficult as possible for someone to access the underside of your car. Parking with the exhaust facing a kerb is ideal, and leaving your car near a fence similarly limits access.
4. Avoid parking with two wheels on the pavement
If you leave your vehicle with two wheels on the pavement and two on the road, you’re making it easier for thieves to access the underside of your car and steal the catalytic converter.
5. Mark your catalytic converter
It’s possible to get a serial number stamped on your cat, which helps identify if it is stolen. A serial number also acts as a visual deterrent for thieves because scrap yards can quickly identify the component as stolen.
6. Get a garage to weld the bolts
Bolts that are screwed on can easily be removed, so it might be worth taking your car to a garage and asking them to weld the bolts on, making it much harder for thieves to steal the cat.
Frequently asked questions
Do diesels have catalytic converters?
Diesel cars must also meet strict emissions standards. However, they do so in a different way. Rather than using a cat, they are fitted with a diesel particulate filter (DPF).
DPFs work similarly and have an almost identical honeycomb structure, though they focus on capturing soot and engine particulates.
Can a catalytic converter unclog itself?
Whether a catalytic converter can unclog itself depends on the severity of the blockage. In theory, it is possible as long as the exhaust system gets hot enough, which requires your help.
Try driving at a high speed (within the speed limit) for a few miles, getting up to 2,500-3,000 RPMs. Doing this may burn off the deposits in the cat that are causing the blockage. If this doesn’t work, you could try cleaning the cat (providing the clog is minor).
Does insurance cover catalytic converter theft in the UK?
As long as your insurance policy covers theft - whether third-party or comprehensive - you should be covered if somebody steals your catalytic converter. It’s worth checking your insurance policy for peace of mind. Additionally, it might be worth investing in a catalytic converter clamp if your policy doesn't cover theft.
How much does it cost to replace a catalytic converter?
On average, a catalytic converter replacement costs £433.80 on FixMyCar. This guide covers the average cost for different car manufacturers and popular models.
Think your catalytic converter needs replacing? FixMyCar can help you find the right garage at the right price.
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