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Common MOT Faults & Failures: 2026/27 Guide

A defect-by-defect walkthrough of the MOT items owners hit most often, graded the way a tester grades them, with the checks you can do at home.

Published by the Serviced247 editorial teamLast reviewed 29 August 2026Reviewed annually and on inspection-manual change

Most MOT failures are not catastrophic mechanical problems. They are worn, dirty, misaligned or blown items that were visible before the test - and a good proportion of them could have been dealt with for a few pounds on the driveway.

This guide works through the defect areas drivers meet most often, explains how the DVSA inspection manual grades them, and separates what you can genuinely check yourself from what needs equipment.

Key takeaways

  • Lighting, tyres, visibility and brakes account for a large share of everyday MOT problems - and several are checkable on the driveway.
  • The same component can produce a minor, major or dangerous defect depending on severity; the grade decides whether you pass.
  • Minor defects still pass, but they are recorded on your MOT history.
  • An advisory usually means the item is close to a threshold and will not last another year.
  • Fixing the cheap, obvious items before the test is the most reliable way to avoid a retest.

How defects are graded

Every defect is recorded as dangerous, major or minor, with advisories used for items that are wearing but still compliant. Dangerous and major both fail the test; minor defects and advisories pass. The same part can produce any of the three grades - a small chip in the swept area of a windscreen may be minor, a large one major.

Lighting and signalling

Bulbs, lenses and aim make up a large share of routine failures, and they are the cheapest things to get wrong. A blown bulb is a fail; so is a cracked lens letting in water, an incorrect colour, or a headlamp aimed too high.

  • Check every bulb: dipped and main beam, sidelights, indicators, hazards, brake lights, rear fog, reversing and number plate lights
  • Brake lights need a second person or a reflective surface - including the high-level brake light
  • Look for cracked or misted lenses and insecure units
  • Headlamp aim needs equipment; if yours have been disturbed, have them checked

Tyres and roadwheels

The legal minimum tread depth for a car is 1.6mm across the central three-quarters of the tread and around the whole circumference. Below that is a major defect. Cuts, bulges, exposed cord, incorrect speed rating or mismatched tyres across an axle can also fail.

  • Check tread across the width, not just in one groove - uneven wear points to alignment or suspension problems
  • Inspect sidewalls for bulges, cuts and perishing, including the inner sidewall
  • Confirm the spare, where one is fitted and required, and that the tyre pressure monitoring warning is not illuminated
  • Mixing radial and cross-ply, or fitting tyres of the wrong specification, is a failure item

Driver's view of the road

Windscreen damage is assessed by size and position. Damage within the area swept by the wipers directly in front of the driver is judged more strictly than damage at the edges. Torn wiper blades, a washer system that does not deliver fluid, and missing or damaged mirrors are all straightforward failures.

  • Top up the washer bottle and check both jets aim onto the glass
  • Replace smearing or split wiper blades before the test
  • Remove obstructions from the swept area - including large dash-cams and air fresheners in the driver's line of sight

Brakes

Brake performance is measured on a rolling road, so this is not something you can self-certify. What you can do is notice the symptoms: a spongy or long pedal, pulling to one side, judder under braking, a parking brake that travels a long way, or a brake warning light that stays on.

The anti-lock braking warning light is itself a test item on vehicles fitted with ABS. A permanently illuminated warning is a failure.

Suspension and steering

Worn bushes, leaking dampers, corroded springs and excessive play in steering joints are common at higher mileages. Symptoms include clonks over bumps, a car that continues to bounce after a dip, uneven tyre wear and vague steering. These need a ramp to assess properly.

Exhaust and emissions

Petrol cars are tested against gas limits; diesels are tested for smoke opacity, and any visible smoke of any colour for a sustained period is a failure. A missing, modified or obviously tampered diesel particulate filter is a failure. Exhaust leaks, insecure mountings and excessive noise also fail.

A fully warmed engine and a run at motorway speeds beforehand genuinely help a marginal diesel. So does not presenting the car cold, first thing on a winter morning.

Structure, plates and identification

Corrosion in prescribed areas, insecure body panels, doors that do not open and close properly, and damaged towbars all feature. Registration plates must be correctly spaced, legible, correctly coloured and secure - non-standard fonts and spacing are an easy, avoidable failure.

What to do before test day

Working through a structured pre-MOT checklist the weekend before the test catches most of the cheap items on this page. For everything else, the honest answer is that a pre-test inspection at a garage costs money but is cheaper than a retest plus a rushed repair.

Sources