Check engine light on?

Car Fault Code Finder

Type in any fault code from your car — P0420, P0171, U0100, anything — and get a plain-English answer: what it means, how serious it is, and what to do next. No ads, no jargon, no account.

Choose how to continue

Free access lets you look up unlimited codes, see what each one means and how urgent it is, build a scan list for your car and save your work. Full access adds the complete diagnosis for every code — likely causes, DIY checks, garage expectations and rough costs — plus a printable garage report and an offline copy of the tool.

Code readoutOBD-II

Format: letter + 4 digits · P = engine B = body C = chassis U = comms

Your car (optional — appears on the report)

Make

Model

Year

Mileage

Notes — symptoms, when it happens

Scan list

Codes you add build up here. If your scanner showed several codes, add them all — this tool spots patterns across codes that point to one shared cause.

Project

Already purchased? Enter your license key

Type a code on the readout to get started. Every lookup gives you:

What it means — in plain English, not workshop-manual speak.
How serious it is — a straight verdict: fine to drive, book it in soon, or stop.
The code decoded — what each character of the code is telling you.
The full diagnosis — likely causes, checks you can do on the driveway, what a garage will do and roughly what it costs. (This part is the paid unlock.)

Don't have your code yet? A basic OBD2 reader from around £10–£20 plugs in under the dashboard of almost any car built since 2001 and reads it in seconds — or ask your garage for the code from their scan.

Likely causes — most common first

Checks you can do yourself

What a garage will do

Rough cost picture

The full diagnosis is the paid bit. Unlock once to see likely causes, DIY checks, what a garage will do and rough costs — for every code, forever. Plus the printable garage report and an offline copy of the tool.

About the Car Fault Code Finder

When your check engine light comes on, the car stores a fault code — a short reference like P0420 or P0171 that points to what went wrong. The trouble is that the code alone tells you almost nothing, and most lookup sites bury the answer under adverts and copy-pasted filler. This tool does one thing well: you type the code, and it tells you in plain English what it means, how worried to be, and what to do about it. Everything runs in your browser — no account, no ads, and your details never leave your device.

Common uses

Check engine light just came on — find out whether you can keep driving or need to pull over, before you panic or ignore it.

Before a garage visit — walk in knowing what the code means and what the usual fix is, so you can have a proper conversation instead of nodding along.

Buying a used car — scan it with a cheap OBD2 reader, look up anything it finds, and know what you'd be taking on.

MOT preparation — emissions-related codes like catalyst and EVAP faults are common MOT failers; catching them early gives you time to fix the cheap cause first.

Making sense of a garage printout — a scan report full of codes becomes a readable picture, including patterns where several codes share one cause.

How to use it

Get your fault code — from a plug-in OBD2 reader (around £10–£20, fits almost any car built since 2001), a garage or MOT printout, or a dashboard message.

Type the code into the readout and press Look up code.

Read the verdict: what the code means and how urgent it is.

If your scan showed several codes, add each one to the scan list — the tool spots combinations that point to a single shared cause, which can save you paying for two repairs when one would do.

Fill in your car's details if you like, then unlock full access for the complete diagnosis, a printable garage report, and an offline copy of the tool.

Frequently asked questions

Is the fault code finder free to use?

Yes. Looking up codes, seeing what each one means, the severity verdict, the code breakdown, building a scan list for your car and saving your work are all completely free, with no ads anywhere. Unlocking full access adds the detailed diagnosis for every code — likely causes, checks you can do yourself, what a garage will do and a rough cost picture — plus a printable garage report and an offline copy of the whole tool.

Which fault codes does it cover?

All standard OBD2 codes: P (engine and gearbox), B (body), C (chassis) and U (communication). The most common codes have full written guides, and any valid code you type — including manufacturer-specific ones — gets decoded character by character so you always learn which system it points to and roughly how urgent it is.

Do I need a scanner or adapter to use this?

You just need the code itself. That might come from a cheap plug-in OBD2 reader, a garage or MOT printout, a dashboard message, or a code someone read for you. This tool then explains what it actually means and what to do about it — it doesn't connect to the car directly.

Can I trust the severity verdicts?

They're honest general guidance based on what each code typically means — enough to know whether to keep driving, book a garage visit soon, or stop. But no website can see your actual car, so treat it as a well-informed starting point, not a substitute for a qualified mechanic. If your engine light is flashing, or the car feels or sounds wrong, get it checked straight away.

What do I get when I unlock full access?

A one-time payment (never a subscription) unlocks the full diagnosis panel on every code, a clean printable garage report you can take to a mechanic so you're never talked into repairs you don't need, and a downloadable offline copy of the whole tool that keeps working on your own computer without this site.