MOT performance
Porsche Boxster vs BMW M3: MOT pass rates compared
In 2023–2024, 82.2% of 65,604 Porsche Boxster MOT tests and 85.7% of 31,544 BMW M3 tests passed first time — 3.5 points in favour of the BMW M3. Once age, mileage and fuel are allowed for, the BMW M3 fails less often than the Porsche Boxster: 0.41× against 0.55× the national rate for comparable cars.
65,604 Porsche Boxster and 31,544 BMW M3 MOT tests, 2023–2024
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| Figure | Value | Basis |
|---|---|---|
| Porsche Boxster: first-time pass rate | 82.2% | ±0.3 pts (95%), n = 65,604 |
| BMW M3: first-time pass rate | 85.7% | ±0.4 pts (95%), n = 31,544 |
| Porsche Boxster: failures vs similar cars | -45% | same age, mileage and fuel = 1.00 |
| BMW M3: failures vs similar cars | -59% | same age, mileage and fuel = 1.00 |
| Porsche Boxster: dangerous defect | 3.7% | n = 65,604 |
| BMW M3: dangerous defect | 3.5% | n = 31,544 |
| Average age at test | 15.7 vs 14.8 years | Porsche Boxster vs BMW M3 |
Why the raw pass rates can mislead
The Porsche Boxster was tested at an older average age (15.7 years against 14.8), and older cars fail more often whatever they are. That is why the table above also shows failures against cars of the same age, mileage and fuel: it compares the models, not their fleets.
Failure areas side by side
Share of MOT tests that failed on each area, and in brackets how that compares with cars of the same age, mileage and fuel (1.00 = national average). The clearest difference is steering, where the Porsche Boxster fails 3.6 times as often on an adjusted basis.
| Area | Porsche Boxster | BMW M3 |
|---|---|---|
| Brakes | 4.1% (-52%) | 3.3% (-64%) |
| Steering | 0.7% (-66%) | 0.2% (-91%) |
| Suspension | 4.2% (-61%) | 3.2% (-73%) |
| Tyres | 3.1% (-42%) | 3.4% (-43%) |
| Road wheels | 0.1% (-61%) | 0.3% (-10%) |
| Lights, reflectors and electrical | 6.5% (-54%) | 4.6% (-70%) |
| Body, chassis and structure | 1.8% (-66%) | 0.8% (-85%) |
| Driver's view of the road | 2.3% (-61%) | 2.1% (-65%) |
| Noise, emissions and leaks | 4.4% (-12%) | 2.4% (-58%) |
| Seat belts and airbags | 0.4% (-75%) | 0.9% (-50%) |
| Registration plates and VIN | 0.4% (-19%) | 0.6% (+23%) |
Pass rate at the same age
Comparing cars of the same age removes most of the fleet-age effect from the raw rates.
| Age at test | Porsche Boxster | BMW M3 |
|---|---|---|
| 3-4 years | 94.4% (n = 2,772) | 92.9% (n = 763) |
| 5-6 years | 94.0% (n = 3,960) | 88.7% (n = 3,357) |
| 7-8 years | 93.2% (n = 4,572) | 88.2% (n = 2,501) |
| 9-10 years | 91.5% (n = 4,968) | 89.3% (n = 1,502) |
| 11-12 years | 90.3% (n = 3,660) | 87.4% (n = 2,440) |
| 13-15 years | 87.8% (n = 5,505) | 87.0% (n = 4,712) |
| 16+ years | 76.0% (n = 39,595) | 83.0% (n = 15,822) |
Most common failure item
- Porsche Boxster · catalyst emissions: lambda reading after 2nd fast idle outside specified limits (2.93% of tests)
- BMW M3 · condition: has ply or cords exposed (1.39% of tests)
MOT results reflect how cars are maintained as well as how they are built, so a gap between two models is a difference in test performance, not proof that one is more reliable. For one car, its own MOT history says more than any average.
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UK number plate or 17-character VIN
About this data. These are MOT test results, not a measure of mechanical reliability: a car's MOT outcome reflects its condition on the day, which depends on how it has been maintained and driven as well as how it was built. Figures cover class 4 vehicles (cars and light vans), normal tests only (retests excluded), outcomes pass, fail and pass after rectification at the station; vehicles at least 2.5 years old at test. Tests from 2023-01-01 to 2024-12-30. “Compared with similar cars” means compared with the national rate for cars of the same age, mileage band and fuel. Contains public sector information licensed under the Open Government Licence v3.0. Makes and models are matched to 73 Auto's vehicle catalogue; tests that can't be matched are left out rather than guessed. See how the MOT figures are produced.