At a glance
How 2,607 first tests went in 2025.
- Passed first time
- 74 in every 100
- Did not pass first time
- 26 in every 100684 failed first-attempt tests
- The typical car
- 10 yearsabout 53,484 miles
- First tests counted
- 2,607
What failed most often
- Individual sidelight or tail light (front)14 in every 100 failed tests
- Petrol emissions (with catalyst)12 in every 100 failed tests
- Suspension arm pins and bushes (front)9 in every 100 failed tests
How we count this. Data: UK MOT open data, 2025. Only Class 4 cars on their first MOT of the year are counted. A car that fails and is fixed at the test station still counts as a fail in the first-attempt rate. These are raw results, not adjusted for age, mileage, or peer mix. The MOT does not test engine or gearbox internals.
These are patterns across 2015 SEAT Mii vehicles in 2025, not a prediction that any one car will have them. Faults are grouped by part of the car. They come from MOT defect codes, not manufacturer bulletins, recalls or a diagnosis of any one car.
Body and structure
One fault: fuel cap, 24 times as often as on similar cars.
Figures below are measured across the 683 of 684 failed first attempts (99.9%) that recorded an odometer reading in 2025. Mileage is needed to compare like with like.
We only list faults with at least 20 failures and a rate of about 2.0 times that of similar cars, which keeps one-off results out of the list.
Fuel cap
What it means
A missing or ineffective fuel filler cap is Major, as is a plain fuel system leak, while a fuel system leaking excessively or a risk of fire has its own, separate wording. A fuel tank with a hole, or a split filler neck, from which fuel can leak must be failed for leaking even if the hole or split is above the fuel line.
Data: UK MOT open data, 2025. Compared with cars of the same age and mileage.
Brakes
Two faults. The strongest is the brake imbalance across an axle (roller test, efficiency check, rear): 6.3 times as often as on similar cars.
Brake imbalance across an axle (roller test, efficiency check, rear)
What it means
A wheel giving less than a set share of the maximum effort from the other wheel on the same axle is Major. On a steered axle, less than half is graded Dangerous. Testers disregard an imbalance if the lower effort is the result of a locked wheel, or if the higher effort from a wheel is at or below a low set figure.
Brake performance (roller test, rear)
Data: UK MOT open data, 2025. Compared with cars of the same age and mileage.
Noise, emissions and leaks
One fault: petrol emissions (with catalyst), 5.0 times as often as on similar cars.
Petrol emissions (with catalyst)
What it means
Emissions levels over the manufacturer's specified limits are Major, as are levels over default limits, which apply when no exact match is found for the vehicle. Dense blue or clearly visible black smoke at idle, held for a set period, is Major, except for certain older vehicles and two stroke engines where smoke is unavoidable. An induction or exhaust leak that could affect emissions levels is Major too.
Data: UK MOT open data, 2025. Compared with cars of the same age and mileage.
Lamps and electrical
Two faults. The strongest is the individual sidelight or tail light (front): 3.9 times as often as on similar cars.
Individual sidelight or tail light (front)
What it means
A position lamp showing red light to the front or white light to the rear is Major. Rear lamps must show a steady red light, and front ones can show white, predominantly white with a blue tinge, or yellow if combined in a yellow headlamp. With a multiple light source, up to half not working is Minor and more than half is Major.
Number plate lights
What it means
Registration plate lamps must light up the rear registration plate and operate at the same time as the position lamps. A missing or inoperative lamp is Major when the plate has only one lamp or all its lamps are not working, and Minor when the plate has several lamps or light sources and not all have failed. A lamp throwing direct white light to the rear is also Minor.
Data: UK MOT open data, 2025. Compared with cars of the same age and mileage.
Suspension
One fault: suspension arm pins and bushes (front), 2.1 times as often as on similar cars.
Suspension arm pins and bushes (front)
What it means
Pins and bushes on suspension arms fail as Major when they are excessively worn. They are graded Dangerous when likely to become detached. DVSA uses the same wording for a suspension joint.
Data: UK MOT open data, 2025. Compared with cars of the same age and mileage.
MOT pass rates
How first tests ended, and how the pass rates are counted.
- Passed first time
- 74in every 100
- Passed on the first test.
- Fixed at the station
- 6in every 100
- Failed, then fixed at the test station the same day.
- Failed
- 20in every 100
- Did not pass, and were not fixed at the test station.
First-attempt pass 73.8% of 2,607 first tests (2025): only cars that passed first time count. Official-style pass 80.2%: cars fixed at the test station also count as a pass. The 6 fixed and the 20 not fixed make the 26 in every 100 that did not pass first time.
Same model, other years
Passed first time in every 100, all tested in 2025.
Newer cars are younger, so look for a jump rather than the climb. A year earlier (2024), when these cars were a year younger, 77 in every 100 passed first time.
| Year | Passed first time | First tests |
|---|---|---|
| 2012 | 70 in every 100 | 1,680 |
| 2013 | 70 in every 100 | 3,370 |
| 2014 | 75 in every 100 | 2,994 |
| 2015 This car | 74 in every 100 | 2,607 |
| 2016 | 74 in every 100 | 2,154 |
| 2017 | 80 in every 100 | 1,436 |
| 2018 | 83 in every 100 | 1,235 |
| 2019 | 84 in every 100 | 1,269 |
If you are buying one
What this year's MOT record means for the decision in front of you.
Mileage matters most on a 2015 SEAT Mii.
Of 2015 SEAT Mii vehicles with under 35,000 miles, 84 in every 100 passed their 2025 MOT first time. With 75,000 miles or more, 62 in every 100 did.
What to check at your mileage
How often each fault turned up on a failed first test, by the car's mileage. Read it as: what is likely to need looking at on a car like the one in front of you.
| Under 35,000 | 48,000–60,000 | 75,000 and over | |
|---|---|---|---|
| Individual sidelight or tail light (front) | 2.5 | 3.6 | 5.9 |
| Petrol emissions (with catalyst) | 1.0 | 3.2 | 4.2 |
| Suspension arm pins and bushes (front) | 1.2 | 3.6 | 3.2 |
| Fuel cap | 1.3 | 1.7 | 3.6 |
| Brake performance (roller test, rear) | 0.0 | 1.9 | 4.9 |
Faults per 100 first tests, by the car's mileage at the test.
When a car fails
of failed cars had one item to fix.
of failed cars had three or more items to fix.
of all first tests had a defect the tester marked dangerous (unsafe to drive away).
Every figure here is a first-attempt MOT rate from DVSA open data for this model line, for cars of this model year tested in 2025. Each mileage band holds a fifth of the tests. MOTs do not test engine or gearbox internals, so this is a pre-purchase checklist, not a full reliability score.
FAQs
Short answers about how to read this model-year guide.
About this data
How this page is built and what it can (and can't) say.
These figures come from UK MOT open data for this model year. We surface common failure patterns against similar cars, not a full reliability score, and not a pass/fail verdict on any individual vehicle.
What we include
UK Class 4 cars only. Normal MOT tests (not retests); first test per vehicle per calendar year; results pass, PRS, or fail.
Same-day repairs
PRS means the car failed items that were fixed at the test station and then passed the same day. We count PRS as a first-attempt fail in headline rates so same-day repairs do not hide problems.
How we compare
We compare this model year with other Class 4 cars of similar age and mileage in the same test year. This model family is left out of the peer group so the car is not measured against itself.
What this does not cover
- MOTs do not cover engine internals, gearboxes, or many electronics; this is not a full reliability score.
- Common faults come from MOT defect stats, not manufacturer TSBs or recalls.
- Age and mileage matching reduces, but does not remove, differences in how cars were used and maintained.
- If the data for a car is too thin to say anything useful, we say so rather than guess.
Contains public sector information licensed under the Open Government Licence v3.0.
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