The top 10 in this list, model by model
1 · 43% fewer MOT fails
Mercedes-Benz GL-Class
Why it ranks here: 43% fewer MOT fails than cars the same age and mileage (ratio 0.57, 95% CI 0.54–0.59), from 8,511 MOT tests at 8 to 12 and 15 years. At typical mileage its rate would be about 17.6% (16.9%–18.4%), against 31.1% for all cars at the same ages; raw (its own ages and mileage) 19.0%. Rank range 1–3.
Check before you buy: no part fails significantly more often than on cars the same age (ages 3 to 15).
Suits: buyers looking at a large SUV; the ones tested were mostly diesel.
2 · 43% fewer MOT fails
Mercedes-Benz S-Class
Why it ranks here: 43% fewer MOT fails than cars the same age and mileage (ratio 0.57, 95% CI 0.56–0.58), from 83,256 MOT tests at 3 to 15 years. At typical mileage its rate would be about 13.6% (13.4%–13.9%), against 23.9% for all cars at the same ages; raw (its own ages and mileage) 14.4%. Rank range 1–3.
Check before you buy: fails on road wheels 2.1–2.5× as often as cars the same age (639 fails in 84,211 MOT tests at ages 3 to 15, not mileage-adjusted); fails on number plates and VIN 1.5–1.9× as often as cars the same age (397 fails in 84,211 MOT tests at ages 3 to 15, not mileage-adjusted).
Suits: buyers looking at an executive car; the ones tested were 71% diesel, 24% petrol.
3 · 41% fewer MOT fails
Mercedes-Benz SL
Why it ranks here: 41% fewer MOT fails than cars the same age and mileage (ratio 0.59, 95% CI 0.57–0.61), from 28,761 MOT tests at 4 to 15 years. At typical mileage its rate would be about 16.6% (16.1%–17.1%), against 28.0% for all cars at the same ages; raw (its own ages and mileage) 13.4%. Rank range 1–3.
Check before you buy: fails on road wheels 1.3–1.8× as often as cars the same age (176 fails in 29,383 MOT tests at ages 3 to 15, not mileage-adjusted).
Suits: buyers looking at a sports car; the ones tested were mostly petrol.
4 · 33% fewer MOT fails
Mercedes-Benz M-Class
Why it ranks here: 33% fewer MOT fails than cars the same age and mileage (ratio 0.67, 95% CI 0.67–0.68), from 93,128 MOT tests at 7 to 15 years. At typical mileage its rate would be about 22.5% (22.3%–22.8%), against 33.4% for all cars at the same ages; raw (its own ages and mileage) 24.1%. Rank range 4–5.
Check before you buy: fails on number plates and VIN 1.3–1.6× as often as cars the same age (488 fails in 94,174 MOT tests at ages 3 to 15, not mileage-adjusted).
Suits: buyers looking at a large SUV; the ones tested were mostly diesel.
5 · 30% fewer MOT fails
Mercedes-Benz GLE
Why it ranks here: 30% fewer MOT fails than cars the same age and mileage (ratio 0.70, 95% CI 0.69–0.72), from 112,225 MOT tests at 3 to 10 years. At typical mileage its rate would be about 11.4% (11.2%–11.6%), against 16.2% for all cars at the same ages; raw (its own ages and mileage) 12.2%. Rank range 5–7.
Check before you buy: fails on number plates and VIN 2.6–3.0× as often as cars the same age (699 fails in 113,268 MOT tests at ages 3 to 15, not mileage-adjusted); fails on road wheels 1.4–1.7× as often as cars the same age (395 fails in 113,268 MOT tests at ages 3 to 15, not mileage-adjusted).
Suits: buyers looking at a large SUV; the ones tested were mostly diesel.
6 · 28% fewer MOT fails
Mercedes-Benz R-Class
Why it ranks here: 28% fewer MOT fails than cars the same age and mileage (ratio 0.72, 95% CI 0.69–0.75), from 4,446 MOT tests at 12 to 15 years. At typical mileage its rate would be about 28.3% (27.0%–29.5%), against 39.2% for all cars at the same ages; raw (its own ages and mileage) 30.5%. Rank range 5–8.
Check before you buy: no part fails significantly more often than on cars the same age (ages 3 to 15).
Suits: buyers looking at an MPV; the ones tested were mostly diesel.
7 · About average
Mercedes-Benz G-Class
Why it ranks here: No clear difference from cars the same age and mileage by our 20% rule (ratio 0.72, 95% CI 0.67–0.78), from 6,435 MOT tests at 3 to 6 years. At typical mileage its rate would be about 9.5% (8.8%–10.2%), against 13.1% for all cars at the same ages; raw (its own ages and mileage) 9.2%. Rank range 4–9.
Check before you buy: no part fails significantly more often than on cars the same age (ages 3 to 15).
Suits: buyers looking at a large SUV; the ones tested were 62% petrol, 38% diesel.
8 · 25% fewer MOT fails
Mercedes-Benz GLC
Why it ranks here: 25% fewer MOT fails than cars the same age and mileage (ratio 0.75, 95% CI 0.74–0.76), from 296,983 MOT tests at 3 to 10 years. At typical mileage its rate would be about 11.7% (11.6%–11.8%), against 15.6% for all cars at the same ages; raw (its own ages and mileage) 12.3%. Rank range 6–9.
Check before you buy: fails on number plates and VIN 1.8–2.1× as often as cars the same age (1,262 fails in 298,696 MOT tests at ages 3 to 15, not mileage-adjusted); fails on suspension 1.25–1.31× as often as cars the same age (8,880 fails in 298,696 MOT tests at ages 3 to 15, not mileage-adjusted).
Suits: buyers looking at a family SUV; the ones tested were 78% diesel, 16% petrol.
9 · 21% fewer MOT fails
Mercedes-Benz E-Class
Why it ranks here: 21% fewer MOT fails than cars the same age and mileage (ratio 0.79, 95% CI 0.78–0.79), from 845,517 MOT tests at 3 to 15 years. At typical mileage its rate would be about 19.4% (19.4%–19.5%), against 24.7% for all cars at the same ages; raw (its own ages and mileage) 20.8%. Rank range 9–10.
Check before you buy: fails on road wheels 3.4–3.6× as often as cars the same age (10,233 fails in 851,495 MOT tests at ages 3 to 15, not mileage-adjusted); fails on number plates and VIN 1.5–1.6× as often as cars the same age (3,623 fails in 851,495 MOT tests at ages 3 to 15, not mileage-adjusted); fails on tyres 1.3–1.4× as often as cars the same age (71,996 fails in 851,495 MOT tests at ages 3 to 15, not mileage-adjusted).
Suits: buyers looking at an executive car; the ones tested were mostly diesel.
10 · About average
Mercedes-Benz GLS
Why it ranks here: No clear difference from cars the same age and mileage by our 20% rule (ratio 0.80, 95% CI 0.76–0.84), from 8,846 MOT tests at 3 to 7 years. At typical mileage its rate would be about 11.8% (11.2%–12.5%), against 14.8% for all cars at the same ages; raw (its own ages and mileage) 12.7%. Rank range 7–15.
Check before you buy: fails on tyres 1.3–1.5× as often as cars the same age (777 fails in 10,285 MOT tests at ages 3 to 15, not mileage-adjusted).
Suits: buyers looking at a large SUV; the ones tested were mostly diesel.
How we rank
5,174,105 MOT tests from 2022–2025 of cars 3 to 15 years old. For each model and age, the tests are split into 6 mileage bands (<30k, 30-60k, 60-90k, 90-120k, 120-150k, 150k+); the expected fails are what all cars of that age would fail in the same bands, corrected to the model's own mix of test years. The ratio of the model's fails to the expected fails sets its place. The adjusted rate is that ratio times the all-car rate at the model's own ages, so it reads against that rate: a model tested only at 3 to 5 years is compared with young cars, not with this list's average.
The 95% intervals cover sampling error only (Wilson intervals). A model is called fewer or more only when its interval is at least 20% from the all-car rate, overall and at 3 or more ages ("close to average" when the interval excludes the all-car rate by less); awards use the same rule. Test years: Each model's expected fails therefore use its own mix of test years 2022–2025, age by age; the mileage bands themselves pool the four years, which can leave a small bias in favour of models first sold late in the window. Generations of a model are pooled unless the data splits them; each row says which years it covers. How we compare
Limitation: MOT tests record roadworthiness defects on the test day. They do not record breakdowns, engine or gearbox faults, or repair costs, and they cannot separate design from upkeep: a model whose owners service it before every MOT looks better here. Only cars still on the road are tested.