AI-Diagnostics-Pro for UK drivers
Instant OBD-II Fault Code Analysis for UK Drivers
Enter your fault code and vehicle details to get a clear UK-focused report with likely causes, whether it is safe to drive, MOT risk, and indicative repair-cost ranges. Built for real UK drivers, not US garages. Reports from £1.59.
Works with generic and many manufacturer-specific OBD-II fault codes.
Browse the most searched fault codes first
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Know if it is safe to drive
See when a flashing or active engine light points to a stop-now issue versus something you can book in.
See likely UK repair-cost ranges
Use indicative parts and labour ranges to compare garage quotes before authorising work.
Understand MOT risk before test day
Check whether the fault is likely to trigger an MOT failure or warning-light problem.
What you get in every paid report
Vehicle-specific summary
The report is generated from your fault code plus your year, make, model, engine, fuel type and mileage.
Safety and urgency guidance
See whether the issue looks driveable, whether it needs quick action, and when a flashing light means stop.
UK repair-cost context
Use indicative parts and labour ranges to sense-check quotes before you approve work.
MOT and next-step advice
Understand likely MOT impact, suggested checks, and what to ask a garage before spending money.
Why you can trust the process
What is an OBD2 fault code?
When your car's check engine light comes on, it means the ECU (Engine Control Unit) has detected a problem and stored a fault code — also called a DTC (Diagnostic Trouble Code). OBD-II fault codes use a standardised format across all major manufacturers, but some codes are generic while others are manufacturer-specific. In the UK, OBD-II is standard on petrol cars from 2001 and diesel cars from 2004, with many late-1990s vehicles also supporting it.
Fault codes start with a letter that identifies the system: P (powertrain — engine and gearbox), B (body), C (chassis) or U (network). This is followed by four digits that identify the specific fault. For example, P0420 means the catalytic converter on Bank 1 is operating below efficiency threshold.
To read your fault code you need an OBD-II scanner — available from £8 on Amazon. Plug it into the 16-pin diagnostic port under your dashboard, turn the ignition on, and the scanner displays any stored codes. You then enter the code into AI-Diagnostics-Pro along with your vehicle details to get your full UK diagnostic report.
Will my fault code fail the MOT?
For vehicles where DVSA MIL checks apply, an illuminated check engine light (malfunction indicator lamp) is a Major MOT failure. The exact rule depends on the vehicle's age and fuel type, so an active fault code should always be checked before test day.
This is why it is important to scan and diagnose your fault codes at least 2 weeks before your MOT — giving you time to fix the fault and clear the code. AI-Diagnostics-Pro includes a specific MOT risk assessment in every report, so you know exactly where you stand before booking your test. Read our full MOT guide for more information.
Why UK-specific repair costs matter
Most online OBD2 resources show US dollar repair costs, which bear no relation to what UK garages charge. UK labour rates, parts prices and MOT requirements are completely different from the US and even from mainland Europe.
AI-Diagnostics-Pro provides indicative UK repair-cost ranges using typical parts and labour references, including VAT. Actual quotes vary by vehicle, region, and garage, so the aim is to help you compare options with better context before authorising work.
Free UK Vehicle Check — Powered by Car Tax Check
Before you repair a fault code, it's worth knowing your vehicle's full history. Our partner Car Tax Check provides a free instant check on any UK registration — covering MOT history, mileage records, vehicle specification, performance data, fuel economy, and current valuation.
Top 15 Most Searched OBD2 Codes in the UK
Click any code for symptoms, causes, UK repair costs and MOT advice — free information on every page.
Frequently asked questions
What does a check engine light mean?
The check engine light (engine management light) means your car's ECU has detected a fault and stored a diagnostic trouble code. It does not tell you what is wrong on its own — you need an OBD-II scanner to read the specific fault code. AI-Diagnostics-Pro then interprets that code and gives you a full UK-specific diagnostic report.
Is it safe to drive with a check engine light on?
If the light is flashing, stop driving immediately — a flashing light usually indicates a serious engine misfire that can cause rapid catalytic converter damage. If the light is solid and steady, it is generally safe to drive short distances, but you should scan the code as soon as possible to understand the risk.
How much does a car diagnostic cost at a garage?
Most UK garages charge between £40 and £120 just to plug in their diagnostic machine and read the codes. AI-Diagnostics-Pro gives you a full AI-generated diagnostic report specific to your vehicle for just £1.59 — a fraction of the cost, available instantly without a garage visit.
Do OBD2 fault codes work on all cars?
They work on OBD-II compatible cars. In the UK that generally means petrol cars from 2001 and diesel cars from 2004 onwards, plus many late-1990s vehicles. Once a car is OBD-II compatible, the standard format is shared across manufacturers, but some fault codes are still manufacturer-specific.
Can I clear a fault code myself?
You can clear a fault code using an OBD-II scanner, but if the underlying fault has not been fixed, the code will return within a few drive cycles. Clearing codes before an MOT test without fixing the fault is not recommended — the code will reappear and the MIL will illuminate, failing the test. Always fix the fault first.
What is the most common OBD2 fault code in the UK?
P0420 (Catalyst System Efficiency Below Threshold) is one of the most common fault codes seen in UK garages. It indicates the catalytic converter is not operating efficiently. Before replacing the catalytic converter (which can cost £400–£800), it is worth checking the oxygen sensors first — a faulty O2 sensor is a cheaper fix that often triggers the same code.
How we present guidance
Repair ranges are indicative UK estimates based on typical parts and labour references. MOT guidance is written for UK drivers and should be read with the vehicle's age, fuel type, and warning-light state in mind. Exact diagnosis and pricing still depend on the vehicle, related faults, and workshop inspection.
Compatible with all major UK car manufacturers
AI-Diagnostics-Pro works with modern OBD-II compatible vehicles, including petrol cars from 2001, diesel cars from 2004, and many later-1990s vehicles. This includes all major manufacturers:
Get Your Full AI Diagnostic Report
Enter your vehicle's year, make, model, engine and fault code.
Get UK repair costs, MOT advice and step-by-step fix guide — instantly.
Why UK Drivers Choose AI-Diagnostics-Pro
Save money before the garage
Know your UK repair cost range before you book so you can compare quotes with better context.
Plain English, not jargon
Every report explains exactly what the code means and what to do next.
Built for UK drivers
UK labour rates, DVSA MOT standards and UK parts pricing — not US data.
Instant — no waiting
Your full AI diagnostic report is generated in seconds. No booking, no garage visit.