Which fuel type fails its MOT on the most dangerous defects? Not diesel

Electric cars have the highest dangerous-defect share of any fuel type, and it holds up even without Tesla in the mix.

MOT DATA · 6 min read

A finer cut than the pass rate figures

Our fuel-type pass rate guide found petrol beats diesel in 83 percent of directly comparable models. That answers how often a car fails, not how bad the fault is when it does. DVSA testers grade every flagged defect as advisory, fail or dangerous, meaning unsafe to drive away, and nationally 5.11 percent of all flagged defects in 2024 got that top grade, as our dangerous-defects-by-model guide found. This guide splits that dangerous share by fuel type instead of by model or brand: 2,350 model and fuel combinations with at least 500 tests and 50 flagged defects each, built from the same DVSA test-item extract behind every model page's own failure list on this site.

The result, weighted by every real test behind it

Petrol: 4.74 percent of flagged defects graded dangerous, from 17,332,573 tests across 1,147 model and fuel pairs. Diesel: 5.44 percent, from 14,443,345 tests across 828 pairs. Hybrid: 6.17 percent, from 951,276 tests across 231 pairs. Electric: 9.51 percent, from 358,992 tests across 134 pairs, double the petrol rate and comfortably the highest of any fuel type. This is not a simple average of models, it is every flagged defect on every qualifying test summed by fuel first, so a handful of high-volume models cannot quietly skew the answer the way they can in a model-count comparison.

Not just Tesla

Our dangerous-defects-by-model guide already flagged the Tesla Model 3 as the single sharpest outlier on this site, at 15.03 percent. Tesla makes up a real share of the UK's electric test volume, so the obvious objection is that one brand is carrying the whole electric figure. It is not: strip every Tesla variant out of the electric total and the rate drops from 9.51 to 7.51 percent, from 282,205 tests across the other 132 model and fuel pairs, still well clear of petrol, diesel and hybrid. The Kia Niro EV variants sit at 10.98 and 12.52 percent, the Volkswagen ID.3 Life at 10.93 percent and the Volkswagen e-Golf at 9.19 percent, none of them a Tesla and all of them above every non-electric figure on this page.

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Named models against a familiar comparison

Hyundai Kona (electric): 7.60 percent, 11,144 tests. Renault Zoe: 6.70 percent, 9,612 tests. BMW i3: 5.93 percent, 15,269 tests. Jaguar I-Pace: 5.72 percent, 16,271 tests. Set against a mainstream petrol model on a similar test volume, the Ford Fiesta sits at 4.80 percent across 1,171,051 tests. Every named electric model here fails its MOT less often in absolute terms than a Fiesta, none of this contradicts the pass-rate story, but when one of these does throw up a flagged defect, DVSA testers are considerably more likely to call it dangerous rather than advisory.

Diesel still beats petrol on this measure, by less than the headline suggests

Comparing the same model sold with both fuel types directly, 326 models had enough tests of each to compare: diesel has the higher dangerous-defect share in 242 of them, 74 percent, petrol in 82, and 2 tie. The average gap is a modest 0.57 points, smaller than the fuel-type pass-rate gap. It is not universal: the BMW 740 (8.40 percent diesel against 3.56 percent petrol) and Volvo S90 (11.17 against 7.56) show diesel clearly worse, while the Ford Tourneo (3.71 percent diesel against 7.93 percent petrol) and Peugeot 508 (6.91 against 9.57) run the other way, petrol worse by an even larger margin. Ford Fiesta itself sits close either way, 5.26 percent diesel against 4.80 percent petrol.

What might be driving the electric figure, and what this data cannot confirm

The DVSA result records what failed, not why. Checking the actual top flagged items behind several non-Tesla electric models turns up the same category repeatedly: tyre defects, seriously damaged tyres, exposed cords, bulges and tears, appear disproportionately often relative to their national rate across the Kia Niro EV, BMW i3, Hyundai Kona, Jaguar I-Pace and Volkswagen ID.3. That is consistent with the widely reported effect of a heavier battery pack and instant torque accelerating tyre wear on electric cars, and a damaged or worn tyre is one of the more common routes to a dangerous grading rather than a plain advisory. This dataset cannot confirm that mechanism on its own, only that the pattern in the failure sheet fits it.

What this means if you are buying one

This is about severity, not frequency, so read it next to a model's own pass rate rather than instead of it. Buying an electric salvage lot, budget extra attention on tyre condition specifically, given how often it turns up as the dangerous item behind this figure, and check the model's own failure-reason list on its Salvage Prophet page for what actually goes wrong on that exact model. Run our free vehicle history checker before you bid either way: full DVSA MOT history, the mileage timeline and any clocking anomalies, on any UK registration, no account needed.

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