Failure Model

Each new 3 Series generation fails its MOT less often than the last

MOT fail rate by vehicle age, split by generation. At the same age, each newer generation fails less often: at 13 years old, the E46 fails about 43% of tests, the E90 about 31% and the F30 about 26%.

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How to read it

Each point is the share of first MOT tests at that age that ended in a fail. The shaded band is the 95% confidence interval: wide bands mean few tests, so treat those points with caution. Click a generation in the legend to hide or show it. The E30 and older group starts hidden because its samples are small.

Why it's harder than it looks

• Survivorship. Old cars still being tested are the ones that survived. Neglected cars have already been scrapped, so fail rates at high ages look better than the cars really were.
• Same age isn't the same year. An E46 was 13 around 2018; an F30 turns 13 around 2025. Changes in testing, mileage and servicing over time land on the generation comparison, so "newer generations fail less" is measured, but "newer cars are better built" is not proven by this alone.
• What counts as a fail. Faults fixed during the test (PRS) are counted as fails. Dealers can fix things on the spot and standalone test centres can't, so counting them as passes would bias the results by where cars get tested.
• Messy model names. The DVSA data records the 3 Series under hundreds of different labels, from "3 SERIES" to "320D M SPORT". Every one has to be mapped to the right model before any counting starts.

Method

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