About & methodology

OBDCode UK exists to make the UK's official vehicle data usable by ordinary drivers: what fault codes actually mean, what cars really fail their MOT on, and what the advisories on a certificate are trying to tell you.

Where the numbers come from

• MOT statistics are computed from the DVSA "Anonymised MOT tests and results" dataset published on data.gov.uk under the Open Government Licence v3.0. Headline make/model tables use the 2025 extract (33,082,397 Class 4 initial tests). Registration-year pages use 95,661,523 eligible initial tests from 2023–2025; retests and appeals are excluded.
• Advisory frequencies come from the same dataset's failure-item files joined to the official DVSA inspection-manual lookup tables.
• Fault code definitions follow the SAE J2012 standard for generic OBD-II codes. Severity ratings, cost ranges and diagnosis ladders are editorial, based on typical UK independent-garage pricing in 2026.
• MOT history checks query the DVSA MOT History API in real time — the same source as the official GOV.UK checker.

How pass rates are calculated

Pass rate = (passes + passes after rectification at the test) ÷ all completed initial tests, per make/model, rounded to one decimal. Models need at least 1,500 tests in the year to get a page, so small samples don't produce misleading figures.

How “years to avoid” rankings are calculated

Older cars naturally fail more often, so raw pass rates cannot fairly rank registration years. Our age-adjusted index compares each model-year cohort with every UK vehicle registered in the same year and tested in the same calendar year. An index of 100 equals the same-age baseline. Each registration-year page needs at least 1,500 tests; lower-scoring years are associations for closer inspection, not proof of a design defect.

Independence & affiliate links

Some pages link to diagnostic tools sold by retail partners. These links are marked, never change our data, and never affect what we recommend you check first (which is usually the free thing).

Contact

Corrections and questions: [email protected]