Diesel vs petrol MOT pass rate by manufacturer: petrol wins for 28 of 31 brands

We split MOT pass rate by fuel within 31 manufacturers. Petrol has the higher first-time rate in 28 of them; only Fiat and Mitsubishi buck the trend.

MOT DATA · 6 min read

A brand-level cut neither of our other two fuel pieces ran

We have already compared petrol against diesel model by model, matching 276 individual cars close in age, and separately ranked all 51 manufacturers on their overall pass rate with no fuel split at all. This is the cut between those two: every model under each manufacturer, added together by fuel rather than compared one pair at a time. We took every model with at least 500 first-time tests of a given fuel, grouped those by manufacturer, and kept the 31 manufacturers with at least 5,000 first-time tests of both petrol and diesel, enough volume on both sides to trust the comparison. 26.6 million first-time tests sit behind the 31 manufacturers here, 14,364,663 of them petrol and 12,271,242 diesel.

Petrol wins in 28 of 31 manufacturers, and the gap is largest at French and budget brands

DS has the widest petrol advantage of any manufacturer with enough volume to count, 78.1 percent against 69.2 percent for diesel, an 8.9 point gap. Dacia (80.1 percent against 71.7) and Suzuki (78.8 against 70.5) are close behind at 8.4 points each, then Citroen (74.2 against 66.7, 7.5 points) and Nissan (75.1 against 68.4, 6.8 points). Kia, Alfa Romeo, Hyundai, Jeep, Skoda, Audi and Porsche all show a petrol advantage of 4 points or more. Even the manufacturers with the smallest gap in petrol's favour, Mazda (0.9 points), Honda (0.4) and Mini (0.1), still land on the petrol side of the line.

The two real exceptions, and one dead heat

Only two manufacturers with enough volume to trust buck the trend. Fiat's diesel fleet tests better than its petrol fleet, 72.1 percent against 71.3, a 0.8 point diesel advantage, and Mitsubishi shows the same pattern more clearly, 72.2 percent diesel against 71.6 petrol. Jaguar is the one true dead heat: 80.2 percent for both fuels, to one decimal place. Every other manufacturer in this dataset, all 28 of the rest, favours petrol.

Why this is not simply "diesel is less reliable"

The diesel fleet behind these figures covers far more ground than the petrol fleet: 98,334 miles average against 66,433 for petrol, weighted across all 31 manufacturers, and mileage is one of the strongest predictors of an MOT failure regardless of what is under the bonnet. Buyers choose diesel for exactly the driving that puts miles on a car, so some of this gap is the fuel type and some of it is simply that diesel cars get driven harder before they reach a test centre. It does not explain all of it: our separate age-and-model-matched comparison found the same direction of effect, petrol ahead in 229 of 276 closely matched model pairs, so the pattern survives even when the mileage gap is narrowed. Treat the size of the gap here as an upper bound, not a clean like-for-like verdict on the fuel itself.

The full ranking, all 31 manufacturers

Ordered by the size of petrol's advantage in percentage points, petrol pass rate first: DS +8.9 (78.1% vs 69.2%), Dacia +8.4 (80.1% vs 71.7%), Suzuki +8.4 (78.8% vs 70.5%), Citroen +7.5 (74.2% vs 66.7%), Nissan +6.8 (75.1% vs 68.4%), Kia +6.5 (80.3% vs 73.9%), Alfa Romeo +5.5 (73.7% vs 68.2%), Hyundai +5.4 (78.6% vs 73.2%), Jeep +5.1 (83.1% vs 78.0%), Skoda +4.7 (81.6% vs 76.9%), Audi +4.4 (83.0% vs 78.6%), Porsche +4.1 (91.2% vs 87.1%), Toyota +3.8 (78.2% vs 74.4%), Volvo +3.7 (78.9% vs 75.2%), Subaru +3.6 (77.3% vs 73.8%), Ford +3.2 (74.8% vs 71.5%), Volkswagen +2.9 (77.2% vs 74.3%), BMW +2.6 (83.3% vs 80.7%), Saab +2.5 (70.0% vs 67.5%), Land Rover +2.5 (81.5% vs 79.0%), Renault +2.3 (67.5% vs 65.2%), Mercedes-Benz +2.2 (81.2% vs 79.0%), Seat +2.2 (78.3% vs 76.2%), Vauxhall +2.0 (72.3% vs 70.3%), Peugeot +1.9 (72.2% vs 70.2%), Mazda +0.9 (75.7% vs 74.8%), Honda +0.4 (77.4% vs 76.9%), Mini +0.1 (81.3% vs 81.1%), Jaguar +0.0, dead even at 80.2% both fuels, Mitsubishi -0.7 (71.6% vs 72.2%, diesel ahead), Fiat -0.8 (71.3% vs 72.1%, diesel ahead).

What this means for a salvage buyer

Choosing between a petrol and diesel lot from the same manufacturer, this data says petrol is the safer bet on first-time MOT reliability for all but two brands, and by a wide margin for several of them. But brand and fuel are both background information next to the individual car in front of you: a diesel with a full service history and honest mileage can easily out-test a neglected petrol from the same manufacturer. Use this to set your expectations before you bid, not to replace checking the actual reg.

Run the actual lot through the Analyzer

Fuel type and manufacturer are two inputs among many. Paste the Copart lot in, let the Analyzer read the real damage from the photos, and check the reg's own MOT and mileage history free before you decide what it is worth bidding.

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