BMW 520i common MOT failures and failure rate
What a BMW 520i fails its MOT on, from real DVSA test data, and the part that resolves each item.
Based on 4,061 MOT tests in DVSA data.
About 11.7% of MOT tests recorded on the BMW 520i in DVSA data end in a failure. The same handful of items account for most of them.
Its most common failure is tyres, which makes up 44.5% of the BMW 520i's failures, followed by tyres, other, visibility/wipers, lamps & electrical. Each item below links to the part that resolves it. Confirm the exact fitment against your registration or VIN before buying, and have safety-critical work done by a competent mechanic.
What it fails on, and why
Tyres fail for tread below the 1.6mm legal limit across the central three-quarters, uneven or exposed-cord wear, or sidewall damage. The tester inspects all four; a single illegal tyre is a fail.
This covers a range of smaller items, from a non-working horn to a warning light left on.
Visibility failures include torn or smearing wiper blades, a washer jet that does not reach the screen, and chips or cracks in the driver's swept area. Blades and washer fluid are quick, cheap fixes.
Lighting is the single most common MOT failure and the cheapest to put right. A blown headlight, brake-light or number-plate bulb, a cracked lens, or a headlamp beam that points too high or low will all fail. Most are a two-minute bulb swap.
A missing, damaged, dirty or incorrectly-spaced number plate, or one using the wrong font, will fail. A replacement plate is inexpensive.
Brake failures cover worn pads and discs, an imbalance between wheels, corroded or scored discs, or a binding caliper. Braking efficiency is measured on a rolling road, so a spongy or pulling brake shows up as a low reading.
Failure rate by year
How the MOT failure rate varies by the car's year of first registration (older examples generally fail more as wear sets in).
The parts that fix each
If your car has just failed, you have 10 working days to fix the items and get a free partial retest. These are the usual parts; confirm the exact fitment against your registration or VIN before buying.
Other models
Sources: DVSA MOT History API: MOT test results and defect data · DVSA MOT testing data for Great Britain