Catalytic-converter replacement cost: diagnose first

Last reviewed · OBDCode UK editorial

FixMyCar currently says a catalytic-converter replacement usually costs £200–£900 fitted. Retrieved 2026-08-14. These figures are what named UK sources published on the retrieval date. They are planning ranges, not a quote for your car. A written estimate for this vehicle is the only figure that counts.

What does this job cost in the UK?

FixMyCar publishes two figures for this job: a usual fitted range of £200–£900, and a marketplace average of £509.20, both including parts and labour. They state the price varies with make, model, the part specified and the labour rate. Both were retrieved on 12 August 2026 and neither is a quote for your vehicle.

What the source publishedFigure
Usual fitted replacement (FixMyCar)£200–£900
Parts and labour. They say the price varies with make, model, the part and the labour rate.
FixMyCar marketplace average£509.20
Their published average including parts and labour.

What that figure does not tell you

The range prices a part swap, not a diagnosis. P0420 is an efficiency result reported by a monitor that compares two oxygen sensors, so an exhaust leak, a failed sensor, a misfire or a fuelling fault can produce it without the converter having failed. Replacing the part while the real cause is still present is not a saving.

  • P0420 is an efficiency result, not proof the converter itself failed.
  • Ask what testing ruled out an exhaust leak, a sensor fault, a misfire or a fuelling fault before you approve the part.
  • A cheap converter that will not last, or one fitted while the engine is still damaging it, is not a saving.

What should you ask before authorising the work?

Ask what testing separated converter efficiency from a leak, a sensor or a fuelling fault before any part is ordered. Then ask which converter position and approval specification the quote covers, whether sensors, gaskets, seized fixings, VAT and the underlying cause are included, and what emissions evidence and warranty you get after the repair.

  • What testing separates converter efficiency from an exhaust leak, sensor, fuelling or misfire fault?
  • Which converter position and approval specification does the quote cover?
  • Are sensors, gaskets, seized fixings, VAT and the underlying cause included?
  • What emissions or signal evidence and warranty will be provided after repair?

Safety boundary

Converter replacement is professional-only workshop work; do not lift or crawl under the car, cut, weld or touch a hot exhaust. For an isolated stored efficiency code with normal operation, use caution only to reach a nearby garage. Stop for a flashing lamp, judder, power loss, overheating, fuel or cabin-exhaust smell, or a loose exhaust.

How do you compare two estimates fairly?

Compare the same diagnosis, parts, labour, VAT, fluids, calibration, disposal and warranty scope — two quotes are only comparable when they cover the same work. Ask each garage to price the diagnosis separately from the repair, and to state what the figure excludes. Do not choose a repair from a warning lamp or fault code alone.

Related guides

Two pages cover the decisions either side of this one. The engine management light guide explains what a steady lamp versus a flashing lamp means before any code is read. The exhaust smell guide matters here because cabin fumes are an exposure risk that outranks a cost question and changes whether the car should be driven at all.

P0420 sits next to two other pages on this site because they share a component or a failure mechanism, not because either diagnoses your car. An exhaust leak ahead of the catalyst can admit outside oxygen and distort the comparison the efficiency monitor relies on. That relation only holds when P0420 is actually stored and the leak is upstream.

These pages share a reviewed component or failure mechanism. The connection is conditional, not a diagnosis of this vehicle.

Conditional mechanism chain. An exhaust leak ahead of the catalyst can admit outside oxygen and distort the oxygen-sensor comparison used by the catalyst-efficiency monitor, contributing to P0420 without proving that the converter itself has failed.

Only when: Treat the advisory-to-code relation as conditional on P0420 actually being stored and on the leak being upstream of the monitored catalyst. An unspecified minor exhaust leak does not establish P0420, and P0420 alone does not authorise catalyst replacement.

Where do these figures come from?

Every figure above comes from a named source with the date we read it, so you can check it yourself rather than take this page’s word for it. The price range is FixMyCar’s published guidance. The MOT record and emissions requirements behind an efficiency code are GOV.UK and DVSA material, listed below with retrieval dates.

General guidance, not professional advice.