The most common reasons cars fail their MOT
Most MOT failures are not dramatic. Lights, tyres, brakes, suspension and visibility account for the bulk of them, and a surprising number are things a driver could have spotted on the driveway the week before.
Updated 14 October 2026
Lights and signals
Lighting faults are consistently among the most common failure items. A blown number plate bulb, an indicator flashing at the wrong rate, or a brake light out are all fails, and every one is visible in minutes with a second person walking round the car.
Headlamp aim is also tested. If a car has been loaded heavily or the suspension sagged, the beam can point too high and dazzle oncoming traffic.
Tyres
Tread below 1.6mm is a fail, but so are cuts deep enough to expose the cords, bulges in the sidewall, and mismatched tyre types on the same axle. A 20p coin is a rough guide: if the outer band is visible when you push it into the tread, the tyre is close to the limit.
Brakes and suspension
Worn pads and discs, corroded brake pipes and imbalanced braking between the left and right are common fails. Suspension faults usually mean worn bushes, broken springs or leaking shock absorbers, often signalled by knocking over bumps or the car pulling to one side.
These are the items that most often appear as an advisory first. If last year’s MOT mentioned "brake pipes corroded" or "slight play in a ball joint", assume it will be a fail this time unless the work was done.
Visibility and the small things
A chip larger than 10mm in the area directly in front of the driver, or 40mm elsewhere in the swept area, is a fail. So are split wiper blades and an empty washer bottle, which is the cheapest MOT failure there is.
Number plates fail if they are cracked, faded, use a non-standard font or have the characters spaced to spell a word. A loose or missing mirror, a horn that does not sound, and a seatbelt that does not lock are all quick checks.
A ten-minute pre-MOT check
Walk round with someone pressing the brake and switching the lights and indicators. Check tyre tread and look for bulges. Top up the washer fluid. Sound the horn. Pull every seatbelt sharply. Start the engine and confirm no warning lights stay on.
Then read the car’s previous advisories. Odomint lists every advisory from every past MOT so you can see exactly what the last tester was worried about before the next one looks.
Common questions
What is the most common reason for an MOT failure?
Lighting and signalling faults are consistently near the top, followed by suspension, brakes, tyres and visibility items such as wipers and windscreen damage.
Can an empty washer bottle fail an MOT?
Yes. The washers must work, so an empty bottle is a fail. It is also the cheapest failure to avoid.
Do advisories turn into failures?
Often. An advisory is a warning that something is wearing. If it is not fixed, it is frequently the reason for a fail at the next test.
Check any car before you buy it
MOT history, every advisory and the full mileage record are free for any UK registration. An Odomint Check adds outstanding finance, insurance write-offs, stolen markers and salvage history, with a £10,000 data guarantee.