Which cars fail their MOT on the most dangerous defects?

Not how often a car fails its MOT, but how severe the fault is. Tesla's Model 3 and BMW's biggest engines top the list against a 5.11% national average.

MOT DATA · 5 min read

A different question from pass rate

Every ranking on this site so far asks how often a car fails its MOT. This asks something narrower: once a fault does get flagged, how likely is the DVSA tester to grade it dangerous, meaning unsafe to drive away, rather than a plain fail or advisory. Nationally, DVSA testers marked 5.11% of every flagged defect this way in 2024. That is one flat number, and it hides a real spread once you split it by make and model. This uses the same DVSA test-item extract already behind every model and brand page's own failure list on this site, which is 2024 only, not the multi-year, 33-million-test range behind the rest of the site's pass-rate figures. We ranked every model with at least 20,000 first-time tests that year, 257 of them, and all 50 manufacturers with a failure-reason page of their own already live on this site. See the same question cut by fuel type for how petrol, diesel, hybrid and electric compare on this measure.

The models with the sharpest dangerous-defect skew

Tesla Model 3 Long Range AWD leads every qualifying model: 15.03% of flagged defects graded dangerous (35,956 tests). Then a run of BMW and premium-SUV derivatives: the BMW 330 at 11.04% (20,902 tests), the 420 at 10.81% (63,105), the 2 Series at 9.77% (21,212), the Mercedes-Benz GLE at 9.76% (29,024), the Mercedes-Benz CLA at 9.63% (57,600), the Volvo XC40 at 9.15% (49,045), the BMW 320 at 9.05% (40,027), the Volvo V60 at 8.45% (32,119) and the Kia Niro at 8.26% (48,666). At the other end: the Suzuki Grand Vitara at 2.82% (21,325 tests), Volkswagen Fox at 3.10% (26,277), Land Rover Defender at 3.12% (105,772), Porsche Boxster at 3.28% (32,366), Mazda MX-5 at 3.32% (91,237), Ford Fusion at 3.39% (52,769), Suzuki Jimny at 3.40% (23,965), Mini at 3.45% (263,320), Toyota RAV4 at 3.47% (30,387) and Porsche 911 lowest of the ten at 3.50% (46,948).

The brands with the sharpest dangerous-defect skew

Pooled across every model each brand sells: Tesla tops every manufacturer at 14.22% (87,077 tests), well clear of Maserati at 9.61% (11,386) and Ssangyong at 6.73% (24,656). Then BMW at 6.68% (1,875,368 tests), Volvo at 6.37% (595,855), Kia at 6.27% (961,462), Mercedes-Benz at 6.10% (1,940,026), DS at 5.95% (44,486), Audi at 5.94% (1,730,182) and Abarth at 5.93% (29,419) round out the top ten. Lowest of the 50: Aston Martin at 2.71% (22,581 tests), Ferrari at 3.09% (14,065), Daihatsu at 3.34% (17,011), Rover at 3.37% (31,173), Subaru at 3.39% (59,549), Isuzu at 3.52% (48,341), Chrysler-Jeep at 3.84% (11,508), Saab at 4.05% (49,404), Toyota at 4.06% (1,711,484) and Suzuki at 4.07% (438,576).

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What might be driving it, and what does not fit the obvious story

The pattern at the top looks like a weight-and-power story: Tesla's Model 3 carries a heavy battery pack and delivers its torque instantly, and the BMW and Mercedes-Benz derivatives near the top are bigger-engined, higher-specification versions within ranges that also include far more ordinary variants. Bigger brakes, wider tyres and stiffer suspension components under more routine stress are a plausible reason a defect on these cars gets graded dangerous more often when the DVSA tester finds one. But the bottom of the list will not let that stand as the whole explanation. The Land Rover Defender is one of the heaviest, most mechanically complex vehicles on UK roads and sits at 3.12%, among the lowest of any model checked. Two Porsches, a 911 and a Boxster, both genuine performance cars, sit in the same bottom ten alongside a Mazda MX-5 and a Suzuki Grand Vitara. Weight and power correlate with a higher dangerous-defect share among family and executive derivatives, but they clearly are not the whole story once you widen the sample, and this data cannot say why on its own.

What this means for a salvage buyer

This says nothing about how often a car fails its MOT, only about the character of the failure once one happens, so read it alongside a model's pass rate rather than instead of it. For a salvage buyer, the practical read is about the failure sheet in front of you: on a model near the top of this list, budget on the assumption that a flagged defect is more likely to be a genuine unsafe-to-drive item rather than a minor advisory, and price the repair accordingly rather than hoping it is cosmetic. On a model near the bottom, a flagged defect is statistically more likely to be the less severe kind, though that is a lean on the odds, not a guarantee for the specific car in the lot. Check the model's own failure-reason list on its Salvage Prophet page for what actually tends to go wrong on that model specifically, not just this national skew.

Check the actual car before you rely on any of this

None of this replaces the reg in front of you. Run our free vehicle history checker before you bid: full DVSA MOT history, the mileage timeline and any clocking anomalies, on any UK registration, no account needed.

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