AI-Diagnostics-Pro decodes your OBD2 fault code and gives you UK-specific repair costs, MOT advice and step-by-step fix guidance — specific to your car's year, make, model and engine. Just £1.59 per report.
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). These codes follow a standardised format and are the same across all major manufacturers. All cars sold in the UK since 1996 use the OBD-II (On-Board Diagnostics II) system.
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.
An illuminated check engine light (malfunction indicator lamp) is an automatic MOT failure under current DVSA testing standards. The MOT tester connects an OBD-II scanner and if any fault codes are active and the warning light is on, the vehicle fails — regardless of how it drives.
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.
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 repair cost estimates based on current UK market data — parts and labour at average UK independent garage rates, including VAT. Independent garages are typically 30–50% cheaper than franchised main dealers for most fault code repairs, and our reports reflect this. You get a realistic cost range before speaking to a garage, so you cannot be overcharged.
Click any code for symptoms, causes, UK repair costs and MOT advice — free information on every page.
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.
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.
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.
Yes. All cars sold in the UK since 1996 (petrol from 2001, diesel from 2004 under UK regulation) use the standardised OBD-II diagnostic system. This means fault codes and the diagnostic port are the same across all manufacturers — Ford, Vauxhall, BMW, Volkswagen, Toyota, Mercedes-Benz, Audi, Renault, Peugeot, Nissan, Honda and all others.
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.
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.
AI-Diagnostics-Pro works with all OBD-II vehicles — every car sold in the UK since 1996. This includes all major manufacturers:
Enter your vehicle's year, make, model, engine and fault code.
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