Most Common MOT Fails: What to Check Before Your Test

22 July 2026

Table of Contents

• What Is the Most Common Fail on a MOT?
  • Why MOT Failures Matter
• Lighting and Signalling: The Top MOT Failure
  • Faulty Bulbs and Headlamp Alignment
  • How to Check Before Your MOT
• Brake System Performance and Brake Pads
  • Brake Discs and Pad Wear
• Tyre Condition and Tread Depth Requirements
  • Legal Tread Depth and Tyre Pressure
• Suspension, Steering and Alignment Issues
  • Suspension Arm and Coil Spring Wear
• Driver Visibility: Windscreen Wipers and Mirrors
• Emissions Test and Exhaust System Failures
  • Fuel System and Dashboard Warning Lights
• MOT Checklist: How to Prepare Your Car
  • Pre-MOT Inspection Steps

Last Updated: July 22, 2026

What Is the Most Common Fail on a MOT?

Lighting and signalling failures consistently top the list of MOT failures across the UK. The DVSA (Driver and Vehicle Standards Agency) data confirms this, yet most of these failures are preventable with a simple pre-MOT inspection. Understanding what examiners check gives you the best chance of passing first time.

Lighting and Signalling: The Top MOT Failure

Lighting and signalling failures represent the most common reason vehicles fail their MOT test. Examiners check not just whether lights work, but whether they're properly aligned, the correct colour, and functioning at the right brightness levels.

Faulty Bulbs and Headlamp Alignment

Headlamp alignment is where many drivers slip up. Your headlamps must point at the correct angle; too high and you'll dazzle oncoming traffic, too low and you won't see the road ahead. The MOT test uses a headlamp aim tester to measure the precise angle of your beam.

Indicator lights must be amber, function smoothly, and flash at the correct frequency. The examiner checks all four corners of your vehicle, and any blown bulb or slow-flashing indicator results in failure. Side lights, rear lights, brake lights, and number plate lights all fall under the same scrutiny. A single faulty bulb anywhere on your vehicle is enough to fail the test.

How to Check Before Your MOT

Start by turning on your headlamps in daylight and walking around the car. You should see light from both headlamps, both side lights, both front indicators, both rear indicators, both brake lights, and your number plate light.

Next, test your brake lights. Ask someone to stand behind the car while you press the brake pedal. Both brake lights should illuminate brightly and simultaneously.

For headlamp alignment, park 10 metres from a wall at night and turn on your headlamps. The beam should point roughly at the wall in front of you, not upward. If the beam seems too high or too low, a garage can adjust it using proper equipment.

Check that your number plate is clean and visible. Dirt or damage that obscures any character will fail the test.

Brake System Performance and Brake Pads

Brake system failures are the second most common reason for MOT failure. The examiner tests brake performance on a rolling brake tester, which measures how effectively each wheel can stop the vehicle. Your brakes must work evenly across all four wheels and meet minimum stopping power standards.

Brake Discs and Pad Wear

Brake pads have a legal minimum thickness of 1.6 millimetres. Once your pads wear below this limit, they'll fail the MOT. Brake discs can become warped, cracked, or worn unevenly, all of which affect braking performance.

The MOT examiner will visually inspect your brake discs and pads through the wheel. If the pads are visibly thin or the discs show signs of damage, the test will fail. The rolling brake tester then measures actual stopping power. If your brakes don't meet the threshold, typically around 50% of your vehicle's weight in braking force per axle, you'll fail.

Brake fluid condition also matters. Old, contaminated, or low brake fluid will trigger warning lights on your dashboard and may cause the brakes to feel spongy or unresponsive.

Tyre Condition and Tread Depth Requirements

Tyre failures account for a significant portion of MOT rejections. The legal minimum tread depth in the UK is 1.6 millimetres across the central three-quarters of the tyre.

Legal Tread Depth and Tyre Pressure

To check your tread depth, use the 20-pence test. Insert a 20-pence coin into the tread groove. If the outer ring of the coin is hidden, your tread is above 1.6mm and legal. If you can see the outer ring, your tread is too shallow and you'll fail the MOT.

Tyre pressure also matters. Underinflated tyres wear faster and reduce fuel efficiency. Overinflated tyres wear unevenly and provide less grip. The correct pressure is listed on a sticker inside your driver's door frame or in your owner's manual.

During the MOT, the examiner checks for uneven wear patterns, bulges, cracks, or embedded objects. Any of these defects will result in failure. Uneven wear often indicates suspension or alignment issues, which may also fail the test if severe.

Suspension, Steering and Alignment Issues

Suspension and steering failures make up a smaller but significant portion of MOT rejections. The examiner tests for excessive wear in suspension components, steering linkage play, and alignment issues that affect vehicle control.

Suspension Arm and Coil Spring Wear

Suspension arms, ball joints, and coil springs wear over time, especially on rough roads or after hitting potholes hard. The MOT examiner uses a pit or ramp to visually inspect suspension components for cracks, corrosion, or excessive movement.

If you grab the wheel at 12 and 6 o'clock and move it side to side, you should feel very little play. Excessive movement indicates worn ball joints or bushings. Coil springs can crack or lose tension, causing one corner of the vehicle to sit lower than the others. A visibly sagging corner is an immediate failure.

Steering linkage must be tight with no excessive play. Worn steering components make the car feel vague or unresponsive and are a safety issue.

Driver Visibility: Windscreen Wipers and Mirrors

Driver visibility is a critical safety requirement. The MOT examiner checks that you can see clearly from the driver's seat in all directions, and that your wipers and washers work effectively.

Windscreen wipers must clear the windscreen effectively without leaving streaks or missed areas. Wiper blades typically last 6-12 months and are inexpensive to replace.

Windscreen washers must work and spray the windscreen. The fluid should be topped up regularly, especially in winter.

Mirrors, both the interior rear-view mirror and the two wing mirrors, must be present, secure, and provide an adequate view. A cracked mirror or one that's come loose will fail the test. The windscreen itself must be free from significant damage in the driver's line of sight.

Emissions Test and Exhaust System Failures

Emissions failures are less common than lighting or brake failures, but they're still a significant reason for MOT rejection. The test measures the level of harmful gases your engine produces.

Fuel System and Dashboard Warning Lights

A faulty fuel system or engine management issue will often trigger a dashboard warning light. The MOT examiner checks for active warning lights before even starting the emissions test. If the check engine light is on, the test stops immediately and the vehicle fails.

Common causes include a loose fuel cap, a faulty oxygen sensor, a blocked catalytic converter, or a failing engine management sensor. A well-maintained engine with regular oil changes, air filter replacements, and spark plug servicing will rarely fail the emissions test.

MOT Checklist: How to Prepare Your Car

The best way to pass your MOT is to prepare your car systematically in the weeks before your test. This checklist covers the most common failure points.

Pre-MOT Inspection Steps

Lighting (30 minutes) Turn on headlamps in daylight and walk around the car. Check that both headlamps, both side lights, both front indicators, both rear indicators, and both brake lights are working. Ask someone to stand behind the car while you press the brake pedal. Both brake lights should illuminate brightly. Turn on hazard lights and check that all four corner indicators flash at the same speed. Check that your number plate light works and the plate is clean and fully visible. Replace any faulty bulbs.

Tyres (15 minutes) Check tyre pressure using a pressure gauge and inflate to the correct PSI listed on your driver's door frame sticker. Use the 20-pence test on each tyre. Visually inspect each tyre for bulges, cracks, or embedded objects. Check that all four tyres are the same size and type.

Brakes (15 minutes) Press the brake pedal firmly. It should feel firm and responsive, not spongy. Check the brake fluid level in the reservoir (usually a translucent plastic container under the bonnet). The fluid should reach the "max" line. Visually inspect the brake discs and pads through the wheel. Pads should be thicker than 1.6mm. Discs should be smooth without cracks or heavy scoring.

Windscreen and Wipers (10 minutes) Clean your windscreen thoroughly inside and out. Check that windscreen wipers clear the glass without streaking. Replace the blades if they leave lines or miss areas. Top up windscreen washer fluid. Inspect the windscreen for large cracks or chips in your line of sight. Check that your interior rear-view mirror and both wing mirrors are secure, clean, and properly adjusted.

Suspension and Steering (10 minutes) Grab the steering wheel at 12 and 6 o'clock and try to move it side to side. There should be very little play. Press down hard on each corner of the car. It should bounce back smoothly. Listen for clunks or rattles when you press on the suspension.

Engine and Emissions (5 minutes) Check that the check engine light is not illuminated on your dashboard. Start the engine and listen for rough idling, excessive noise, or smoke from the exhaust. Check that your oil level is adequate using the dipstick.

General Checks (5 minutes) Ensure your number plate is clean, fully visible, and securely attached. Check that your horn works. Verify that your seatbelts work smoothly and latch securely. Check that your handbrake holds the car on a slope.

If you find any issues during this checklist, address them before your MOT appointment. Many repairs are simple and inexpensive when caught early.

What Happens If Your Car Fails

If your car fails the MOT, you'll receive a failure certificate listing the specific defects. You then have a set period (typically 10 working days) to get the issues fixed and return for a re-test.

The re-test is usually cheaper than the full MOT fee, as the examiner only checks the items that were originally failed. Some failures are more serious than others. A faulty bulb might take 10 minutes to fix; a suspension issue might take a day or more. The failure certificate will specify whether each defect is a "failure" (safety-critical) or an "advisory" (not yet critical but worth monitoring).

MOT failures don't have to derail your plans. Most common failures are preventable with a simple pre-test inspection and timely maintenance. Kettering Motorist Centre offers comprehensive MOT testing and pre-MOT inspection services across Kettering and Northamptonshire, with hassle-free online booking and no upfront payment required. Our experienced technicians identify issues before they become test failures, saving you time and money. Book your MOT with Kettering Motorist Centre today and drive with confidence knowing your vehicle meets all safety and emissions standards.

For electric and hybrid vehicle owners, our sister site KMC Electric provides specialist MOT and servicing expertise tailored to battery-electric and plug-in hybrid powertrains.

[EXTERNAL_LINK: DVSA MOT test standards and regulations | dvsa.gov.uk]

[EXTERNAL_LINK: UK Road Traffic Act tyre tread depth legal requirements | legislation.gov.uk]

[EXTERNAL_LINK: Vehicle emissions testing standards and limits | gov.uk]