Most Common MOT Failure Reasons & How to Prepare

MOT Failure Rates in the UK

Around one in three cars fail their MOT on the first attempt. That figure might sound alarming, but many of these failures are for relatively minor, inexpensive issues that could easily have been fixed before the test. A blown headlight bulb, a worn wiper blade, or a tyre slightly below the legal tread depth can all result in a failure — and all cost very little to put right.

Understanding the most common MOT failures is one of the simplest ways to avoid unexpected costs and the inconvenience of a retest. With a little preparation, many of the issues that catch drivers out can be identified and resolved at home before the car ever reaches the test centre.

Checking your MOT history on CheckMyReg can also reveal past advisories — items that were noted as beginning to wear but had not yet reached the failure threshold. These advisories are often the failures waiting to happen at your next test.

The 10 Most Common MOT Failures

Based on DVSA data, these are the ten most frequent reasons vehicles fail the MOT test in the UK, ranked from most to least common:

1. Lights and Signalling

Lighting faults are consistently the number one reason for MOT failure. This includes blown bulbs in headlights, brake lights, indicators, fog lights, and number plate lights. Misaligned headlights and cracked or damaged lenses also cause failures. The fix is usually simple and cheap: walk around the car before the test and check every light is working. Have someone press the brake pedal and activate the indicators while you check from the outside.

2. Suspension

Worn shock absorbers, damaged coil springs, and deteriorated bushings are common failure points, especially on older vehicles and those that regularly drive on rough roads. Signs of suspension trouble include a bouncy ride, the car leaning excessively in corners, and knocking or clunking noises when driving over bumps. Suspension repairs can be costly, so identifying issues early is important.

3. Brakes

Brake-related failures cover a wide range of issues: worn brake pads and discs, seized callipers, leaking brake fluid, corroded brake lines, and imbalanced braking where one side pulls harder than the other. You can often feel brake problems while driving — the car may pull to one side under braking, the pedal may feel spongy, or you may hear grinding or squealing noises.

4. Tyres

Tyres fail the MOT for several reasons: tread depth below the legal minimum of 1.6mm across the central three-quarters of the tyre, sidewall damage such as bulges or cuts, incorrect tyre size for the vehicle, and mismatched tyres on the same axle. A quick check with a 20p coin can verify tread depth — insert the coin into the tread and if the outer band of the coin is visible, the tyre is likely below the legal limit.

5. Driver's View of the Road

This category includes worn or perished wiper blades, insufficient screenwash, and windscreen damage within the driver's swept area. A crack larger than 10mm in the area swept by the wipers directly in front of the driver will cause a failure, as will a crack larger than 40mm anywhere else in the swept area. Topping up screenwash and replacing wipers are among the cheapest pre-MOT fixes.

6. Exhaust Emissions

Vehicles must meet specific emissions standards during the MOT. Petrol cars are tested for carbon monoxide and hydrocarbons, while diesel vehicles undergo a smoke opacity test. Common causes of failure include a damaged or inefficient catalytic converter, a faulty lambda (oxygen) sensor, and general engine wear. Older diesel vehicles are particularly prone to emissions failures. A good run on the motorway before the test can help clear the exhaust system.

7. Steering

Excessive play in the steering, worn track rod ends, damaged steering rack boots, and power steering fluid leaks all result in MOT failure. If the steering feels loose, wanders at speed, or you notice fluid under the car near the front wheels, have the steering checked before the test.

8. Body and Structure

Excessive corrosion to structural components, sharp edges that could cause injury to pedestrians, and insecure body panels are all failure items. This is particularly relevant for older vehicles. Rust on non-structural panels is generally acceptable, but corrosion near suspension mounting points, sills, or chassis members will result in failure.

9. Registration Plates

Number plates must be clearly legible, use the standard font and character spacing, and conform to the correct format. Faded, cracked, or dirty plates that cannot be easily read will fail. Non-standard spacing used to create words or names from the registration is also illegal and will cause a failure.

10. Seatbelts

Frayed or damaged webbing, faulty retractor mechanisms, buckles that do not latch securely, and missing seatbelts all cause failures. Check that every seatbelt in the car pulls out smoothly, retracts properly, and locks securely into its buckle.

Understanding MOT Defect Categories

Since May 2018, MOT defects have been classified into four categories. Understanding these categories helps you interpret your MOT results and know what action is required:

All defect categories are shown on the MOT record, including on the results available through CheckMyReg's MOT history check. Reviewing these records gives you a complete picture of a vehicle's condition over time.

How to Prepare Your Car for the MOT

A simple pre-MOT check at home can save you time, money, and the hassle of a retest. Work through this checklist before taking your car to the test centre:

Spending fifteen minutes on this checklist before the test can eliminate many of the most common failure reasons. Items like blown bulbs, empty screenwash, and worn wipers cost very little to fix but account for a large proportion of MOT failures each year.

Check Your MOT History for Clues

One of the most effective ways to prepare for an upcoming MOT is to review the results from previous tests. Advisories from your last MOT are often a reliable predictor of what will fail next time.

For example, if your last MOT included an advisory for "brake pads wearing thin", there is a strong chance that the pads have now worn below the acceptable threshold and will be flagged as a major defect. Similarly, an advisory for "tyre approaching minimum tread depth" could well have become a failure item after another year of driving.

CheckMyReg shows the full advisory and defect history for any vehicle, making it easy to see what was flagged previously and take proactive action. This is particularly valuable when buying a used car — a vehicle with a long list of advisories may be storing up expensive repairs.