Why MOT failure data matters — and how to use it

Every year around 30 million MOT tests are carried out in the UK, and roughly a third of first-time tests end in a failure. Those aren't evenly distributed — some makes and models are dramatically more likely to fail than others, and within any single model the failure rate rises sharply with age. Understanding which categories your your car is most likely to trip up on isn't just interesting trivia: it's the single most useful pre-MOT preparation you can do, because six out of the top seven failure categories are things you (or a mechanic) can identify and fix in advance for a fraction of the cost of a test-day retest.

Where this data comes from

All MOT tests in Great Britain are recorded in real-time on the DVSA's central MOT Testing System. The DVSA then publishes aggregate statistics annually as part of its open data programme, broken down by make, model, vehicle age, and failure category. The data is as close to definitive as it gets — every test counts, there's no sampling bias, and the classification of failure reasons uses the official MOT Inspection Manual categories. The figures on this page come directly from those published datasets under the Open Government Licence v3.0.

The seven failure categories that account for most MOT failures

Across the UK fleet, just seven categories generate the vast majority of MOT failures. In descending order of prevalence:

  1. Lamps, reflectors and electrical equipment — around 30% of failures. Usually a single blown bulb, a broken number plate light, a misaligned headlamp, or a rear reflector missing after a knock.
  2. Suspension — around 18%. Worn bushes, leaking shock absorbers, split gaiters on ball joints, corroded subframes.
  3. Brakes — around 15%. Worn pads or discs, sticking calipers, imbalanced braking effort between left and right, worn brake hoses.
  4. Tyres — around 10%. Below 1.6mm tread depth across the central three-quarters, sidewall damage, wrong speed rating, tyres of mixed types on the same axle.
  5. Steering — around 7%. Play in track rod ends, worn or split CV boots, leaking power steering racks on older hydraulic systems.
  6. Driver's view of the road — around 5%. Chips or cracks in the driver's A-zone of the windscreen, wipers that don't clear effectively, missing mirrors.
  7. Issues identified during registration and VIN check — around 3%. Number plates that don't meet the current spec, illegible VINs, incorrect chassis marks.

The remaining failure categories — body, seat belts, exhaust, fuel, emissions, horn, battery, tow bar — together account for around 12% of failures. Emissions failures are the one category where DIY fixes rarely help; if your car is emitting too much NOx, CO or particulates, you almost always need a diagnostic visit to a specialist.

How to avoid a failure: the 15-minute pre-MOT walkaround

Around three-quarters of first-time MOT failures come from issues that cost pennies to fix at home. A proper pre-MOT walkaround takes about 15 minutes and catches most of them:

  • Walk around the car with a helper pressing each brake, lamp, and indicator in turn. Note any bulb that doesn't come on or is noticeably dimmer than its pair.
  • Check the tread depth across all four tyres with a 20p coin — the outer band of the coin should be obscured when you push it into the tread.
  • Top up washer fluid and test the wipers clear the screen in one sweep without streaking or squeaking.
  • Check the horn works. It's a surprisingly common failure for buttons that never get used.
  • Look under the front edge for oil drips, grease splattered up behind wheel arches, or a split CV joint gaiter showing fresh grease streaks. These all indicate work that needs doing.
  • Look at the windscreen from the driver's seat — any chip or crack more than 10mm in the A-zone (swept by the driver's wiper, centred on the wheel) is an automatic failure.
  • Check number plates are clean, correctly spaced, and meet the current 3D/4D character-height rules.

Why older cars fail more often

The fail rate climbs steadily with age almost regardless of make. A typical three-year-old car has a fail rate around 10-15%, rising to 25-30% at eight years, 35-40% at 12 years, and 45-55% at 17+ years. This isn't because older cars are inherently badly made — it's corrosion. UK winters, road salt, and our love of the potholed B-road combine to attack brake lines, suspension components, body sills, and subframes at a rate that gradually outpaces the kind of preventive maintenance most owners are willing to pay for. A 15-year-old car with a documented history of underbody treatment and regular suspension inspection fails no more often than one half its age.

Make and model matters — but less than you think

The gap between the best and worst performers on any like-for-like comparison (same age, same mileage class) is typically 10-15 percentage points. That's real but not enormous — a 5% better fail rate on a Honda Jazz compared to a Vauxhall Corsa doesn't make the Corsa a bad car, it just means you're a little more likely to need a £200 fix on MOT day. The bigger lesson from the failure data is that care matters more than badge: a well-maintained, regularly-serviced car of any make will out-pass a neglected one of the best make on any given MOT morning.

What to do if your your car fails

A failed MOT isn't a final verdict — it's a to-do list. You have ten working days to get the work done and return the car for a partial retest, which is free if done at the same garage. Most fails are resolved in an hour or two; only serious chassis corrosion, major brake component replacement, or emissions-system failure tends to take longer. Always get a written copy of the failure reason list with the specific inspection manual codes — you can then shop around different garages for quotes if the fail is substantial, and you'll know exactly which items were outside tolerance versus merely advisory.

If you want to avoid the failure in the first place, book a pre-MOT inspection — many independent garages offer these for £30-£50 and they'll catch 90% of what a formal MOT would flag. A quick MOT expiry check will tell you when yours is due, and Fixaroo lists hundreds of local garages with pre-MOT inspection slots available to book online.