A catalytic converter quietly cleans your exhaust for years, until a warning light, a failed MOT or a sudden roar from under the car tells you something is wrong. Here's what a catalytic converter replacement costs in the UK, the signs it's failing, why cats fail early, what to do about theft, and how a warranty fits in.
What a catalytic converter does
The catalytic converter, or "cat", sits in the exhaust between the engine and the silencer. Inside is a honeycomb coated with precious metals: platinum, palladium and rhodium. As hot exhaust gas passes through, those metals trigger chemical reactions that turn harmful carbon monoxide, unburnt fuel and nitrogen oxides into less harmful carbon dioxide, water vapour and nitrogen.
Diesels use a similar oxidation catalyst, often packaged with the diesel particulate filter. Oxygen sensors before and after the cat tell the engine computer how well it is working, which is why a tired cat usually shows up as a warning light long before you notice anything else.
Catalytic converter replacement cost: typical UK prices
The cost of a catalytic converter depends on the car, whether you choose an aftermarket or a manufacturer (OEM) part, and how hard it is to reach. The ranges below are typical UK garage estimates, fitted, including VAT. Your garage's quote for your car is what counts.
| Car type | Aftermarket part, fitted | OEM part, fitted |
|---|---|---|
| Small petrol car (city car, supermini) | £250 – £600 | £500 – £1,000 |
| Family or executive petrol car | £400 – £900 | £800 – £1,800 |
| Diesel (oxidation cat on its own) | £400 – £1,000 | £800 – £1,800 |
| Diesel (cat and DPF combined unit) | £800 – £1,500 | £1,500 – £3,000+ |
| Hybrid (e.g. Toyota, Lexus, Honda) | £700 – £1,500 | £1,200 – £3,000+ |
| Performance or twin-cat engines | £800 – £2,000 | £1,500 – £4,000+ |
Hybrid cats are pricier because they carry more precious metal. That same metal is exactly why hybrids are the favourite target for thieves. For diesels with a combined unit, our guide to DPF replacement costs goes into more detail, and our repair costs hub compares other big-ticket repairs.
Aftermarket or OEM? A good-quality aftermarket cat that is type-approved for your car can be a sensible choice and will pass an MOT. The cheapest universal units sometimes struggle to keep the rear oxygen sensor happy, bringing the warning light back. Ask your garage which brand they fit and how long the part's own warranty lasts.
Signs of a failing catalytic converter
- Engine management light, often with a fault code such as P0420 or P0430 ("catalyst efficiency below threshold").
- Rotten-egg smell from the exhaust, caused by sulphur compounds the cat is no longer converting.
- Loss of power and poor acceleration, especially uphill, when a blocked cat chokes the exhaust.
- Rattling from underneath, particularly at idle or start-up, when the internal honeycomb has broken up.
- A failed MOT emissions test.
A P0420 code doesn't always mean a new cat. A faulty oxygen sensor or an exhaust leak can give the same reading for a fraction of the cost, so ask for a proper diagnosis before agreeing to a replacement.
Why catalytic converters fail early
A healthy cat can last well over 100,000 miles. When one fails early, there is usually another problem behind it:
- Engine misfires. Unburnt fuel reaches the cat and burns inside it, overheating and melting the honeycomb. A misfire left alone for a few weeks can destroy a cat.
- Oil or coolant burning. Worn piston rings, valve stem seals or a failing head gasket send oil or coolant into the exhaust, coating the cat until it stops working.
- Lots of short trips. A cat needs heat to work and to burn off deposits. Cars that rarely get properly warm can clog up over time, much like a DPF.
- Physical damage. Speed bumps, kerbs and potholes can crack the casing or the brittle ceramic inside.
Fixing the root cause matters. Fit a new cat to an engine that is still misfiring or burning oil and you'll be paying for another one before long.
Catalytic converter and the MOT
The MOT emissions test measures what comes out of the tailpipe. A cat that isn't converting properly will usually push carbon monoxide or hydrocarbon readings over the limit, which is a fail. An engine management light that is on is also a fail on cars first used from 2003. And if the tester finds that a cat fitted as standard has been removed, the car fails as well.
Removing or "deleting" a catalytic converter isn't a cheap fix. It makes the car fail its MOT and puts it outside the law for road use. Our guide to the most common MOT failures covers the other areas testers look at.
Catalytic converter theft
Cat theft took off because of the value of the metals inside. A thief with a battery-powered cutter can remove one in minutes.
Cars most often targeted include older Toyota Prius and Auris hybrids, Lexus RX and other Lexus hybrids, and the Honda Jazz.
Ways to make your car a harder target:
- Park in a locked garage, or in a well-lit spot close to a wall or kerb so the exhaust is hard to reach.
- Ask a garage about a cat lock, cage or shield bolted over the converter.
- Mark the cat with a forensic marking kit or your registration, so it is harder to sell on.
- Consider an alarm with a tilt sensor, which sounds if the car is jacked up.
If your cat is stolen, report it to the police and get a crime reference number. Theft is a crime, not a mechanical breakdown, so it is a matter for the police and your motor policy provider. A mechanical breakdown warranty does not pay for theft. If you drive a hybrid, see our guides to hybrid battery health and hybrid and PHEV warranties.
Catalytic converter cost for popular UK cars
The table above groups cars by type. If you would rather see a figure for a specific model, these are typical fitted prices for an aftermarket, type-approved catalytic converter at a UK independent garage, including VAT. They are estimates rather than quotes: the exact engine, and whether the cat is built into the exhaust manifold, can move the price a long way.
| Car | Aftermarket cat, fitted (typical) |
|---|---|
| Ford Fiesta 1.0 or 1.25 petrol | £300 – £600 |
| Vauxhall Corsa 1.2 or 1.4 petrol | £300 – £600 |
| Volkswagen Golf 1.4 or 1.5 TSI | £450 – £900 |
| Nissan Qashqai 1.5 dCi (cat only, not DPF) | £450 – £1,000 |
| BMW 3 Series 2.0 petrol | £600 – £1,300 |
| Toyota Prius or Auris hybrid | £700 – £1,500 |
A manufacturer (OEM) part usually costs one and a half to two times as much. Main dealers almost always fit OEM parts.
P0420 code: what to check before replacing the cat
The code most drivers see is P0420 (or P0430 on the second bank of a V6 or V8), which means the engine computer thinks the cat is no longer cleaning the exhaust well enough. It is a judgement made from the oxygen sensor readings, not a direct measurement, so a good garage will rule out the cheaper causes first:
- A faulty downstream oxygen sensor. A lazy or contaminated sensor can trigger the code on its own. A sensor usually costs £80–£200 fitted.
- An exhaust leak before or near the sensors, which lets in air and confuses the readings. A cracked flexi joint or a blowing gasket is much cheaper than a cat.
- A misfire or a rich-running engine. Coil packs, spark plugs, injectors or a leaking injector seal can all overwhelm the cat. Fix these first, or the new cat will fail too. Our guide to the engine management light covers the usual culprits.
- Software. On some models the manufacturer has released an engine software update that changes how the cat is monitored.
If all of that checks out and the code keeps coming back, the cat itself is the likely cause.
How long does a catalytic converter last?
On a well-maintained petrol car, a catalytic converter can last 100,000 miles or more, and many last the life of the car. Cats that fail early nearly always have a reason: misfires, oil or coolant burning, lots of short journeys or physical damage, as explained above. Diesels and hybrids follow the same rule, although a diesel's cat often shares a housing with the DPF and is replaced with it.
Can you clean a catalytic converter?
Sometimes, a little. Fuel-system cleaners poured into the tank and a long, steady motorway drive can help a cat that is lightly clogged with deposits, and they are cheap enough to try. They will not repair a cat that has melted, cracked or broken up inside, and they will not cure the misfire or oil burning that caused the damage. Specialist off-car cleaning services exist, but they are usually aimed at diesel particulate filters rather than petrol cats. If a cleaner has not cleared the code after a couple of tanks, stop spending money on it and get a proper diagnosis.
Does a car warranty pay for a catalytic converter?
It depends on the warranty and the cause. A cat that has worn out gradually or been damaged by a knock is not a sudden mechanical failure. Exclusions such as wear items also matter; our guides to wear and tear and what isn't covered by a car warranty explain how providers draw the line.
For ClearPath Premium, whether a catalytic converter or exhaust part is included is set out in your cover schedule, so check it rather than assuming either way. The schedules are on our what's covered page. A warranty can still help with the cause: if a covered engine part fails and leads to misfiring, the repair to that part is assessed on its own merits. Claims pay up to £3,000 per eligible claim, including parts, labour and VAT, with a £100 excess.
Whatever you're claiming for, the garage must contact ClearPath and get authorisation before any work starts. Our make a claim page explains the steps. The Validation Certificate, Warranty Terms & Conditions and your What Is Covered schedule always decide the outcome.
The bottom line
A catalytic converter replacement can cost anything from a few hundred pounds to over £3,000, with hybrids and diesel combined units at the top. For cover against the sudden failure of expensive mechanical parts, compare our plans, read about our used car warranty and hybrid car warranty, or see common diesel problems if you run a diesel.
