Common MOT Failure Points: A 2026 Guide

12 August 2026

Table of Contents

• The Most Common MOT Failure Points
  • Lighting and Signalling Systems
  • Brake System Performance and Wear
  • Tyre Condition and Tread Depth
  • Suspension and Steering Components
  • Emissions and Exhaust System
  • Driver Visibility and Windscreen Issues
• MOT Checklist for Car Owners
  • What to Check Before Your Test
  • How to Spot Advisories vs Major Defects
• Electric Vehicle MOT Requirements
• The 10-Day Rule Explained
• DIY Pre-MOT Checks vs Professional Inspection
• How to Avoid MOT Failure
• Conclusion

Last Updated: August 12, 2026

The Most Common MOT Failure Points

Understanding what causes MOT failure is the most practical thing any car owner can do. You'll save money by fixing problems before your test and avoid the frustration of a failed appointment. At Kettering Motorist Centre, we've seen every type of MOT failure imaginable, and the vast majority are preventable with basic maintenance and inspection.

The MOT test checks your vehicle's roadworthiness across multiple systems. When a component fails, it's classified as either a dangerous defect, a major defect, or an advisory. A dangerous defect means your vehicle cannot be driven. A major defect requires repair before the car can pass. An advisory is something to monitor but doesn't prevent your MOT pass.

Most failures cluster around a small number of systems. Focus your pre-MOT checks on these areas, and you'll eliminate the majority of potential issues.

Lighting and Signalling Systems

Headlights, brake lights, and indicators fail the MOT test more often than expected. A blown bulb is obvious, but alignment and lens damage are equally common culprits.

Your headlights must point in the correct direction. If they're misaligned, they won't pass the MOT even if bright. This happens after minor collisions, pothole impacts, or vibration over time. A technician uses a headlight beam setter to verify alignment precisely.

Check your lights regularly:

• Turn on headlights in daylight and walk around your car
• Look for cracks, discolouration, or condensation inside the lens
• Test every bulb: headlights, brake lights, reversing lights, indicators, and fog lights
• Verify that brake lights illuminate when you press the pedal
• Confirm indicators flash at roughly one flash per second

Indicator bulbs that flash too slowly or too quickly will fail, usually indicating a bulb failure or faulty flasher unit. Lens damage is particularly common on older vehicles; even small cracks create a fail. Replacement is straightforward and inexpensive compared to retesting costs.

Brake System Performance and Wear

Brakes are safety-critical, so the MOT test is rigorous. Your brake discs must have sufficient thickness, brake pads must have adequate material, and the system must generate enough stopping power.

Brake disc thickness is measured with precision equipment. Most modern cars require at least 2mm of material remaining. If you hear a high-pitched squealing sound when braking, your pads are likely worn to the wear indicators, a metal tab designed to alert you.

Brake fluid also matters. Over time, brake fluid absorbs moisture from the air. When moisture content becomes too high, the boiling point drops and braking performance degrades. The MOT test uses a brake fluid tester to check moisture levels.

Common brake failures include worn pads below 1.5mm thickness, discs scored or below minimum thickness, uneven pad wear, contaminated brake fluid, excessive handbrake travel, and illuminated brake warning lights. Check your brakes monthly. Listen for squealing or grinding sounds and feel for soft or spongy brake pedal feedback. If the pedal travels too far before stopping the car, have the system inspected immediately.

Tyre Condition and Tread Depth

Tyres are inspected for tread depth, damage, and wear patterns. The legal minimum tread depth in the UK is 1.6mm across the central three-quarters of the tyre. Modern research suggests you should replace tyres at 3mm tread depth for better wet-weather grip.

The MOT test uses a tyre tread depth gauge to measure precisely. A manual gauge is inexpensive and simple to use at home. If any measurement reads 1.6mm or less, the tyre fails.

Look for uneven wear across the tyre width (suggesting alignment problems), excessive wear on outer edges (usually underinflation), excessive wear in the centre (usually overinflation), visible cords or canvas, bulges or blisters in the sidewall, cracks or cuts larger than 25mm, and incorrectly repaired punctures.

Check your tyre pressure monthly. Underinflated tyres wear faster, reduce fuel economy, and generate heat. Overinflated tyres wear unevenly and provide a harsher ride. Your vehicle's recommended pressure is printed on a sticker inside the driver's door.

Suspension and Steering Components

Suspension wear is checked by applying force to the wheel and measuring movement. Excessive play indicates wear in bushes, ball joints, or shock absorbers. A technician uses a suspension tester to measure this movement objectively.

Common suspension failures include worn suspension bushes, damaged or leaking shock absorbers, worn ball joints, steering rack damage, and loose anti-roll bar links. Grasp the wheel at the 3 o'clock and 9 o'clock positions and apply firm pressure. Excessive movement suggests worn components. Any clunking sound warrants professional inspection.

Steering play is also tested. Turn the steering wheel and feel for excessive movement before the wheels respond. If the steering wheel turns more than 40mm before the wheels move, the steering rack likely needs attention.

Emissions and Exhaust System

The emissions test measures carbon dioxide (CO2), carbon monoxide (CO), and hydrocarbon (HC) levels in your exhaust. Vehicles must meet Euro 6 standards. A diesel smokemeter also checks for visible smoke.

Exhaust system failures typically indicate engine problems. A faulty oxygen sensor, damaged catalytic converter, or engine tuning issues can cause high emissions. If your check engine light is illuminated, have the vehicle scanned before your MOT.

Common exhaust failures include visible leaks in the exhaust pipe or silencer, rust holes, loose or missing silencer, damaged catalytic converter, emissions levels exceeding legal limits, and visible smoke from the exhaust. A pre-MOT emissions scan can help identify issues before your official test.

Driver Visibility and Windscreen Issues

The windscreen must be free from damage that obstructs the driver's view. Cracks or chips in the driver's line of sight are automatic fails. Damage in other areas may pass if it doesn't obscure vision.

Windscreen wipers must work effectively. Worn wiper blades should be replaced every six to twelve months. Check that all mirrors are intact and correctly adjusted, and ensure rear window visibility isn't obscured. A small chip in the wrong location can fail your MOT. If you have damage to the driver's line of sight, have the windscreen replaced before testing.

MOT Checklist for Car Owners

A structured pre-MOT inspection saves time and money. Work through this checklist systematically to identify most common issues before your appointment.

What to Check Before Your Test

Start with the basics. These checks take thirty minutes and cover the most common failure points.

Exterior inspection:

• Walk around the vehicle and look for visible damage
• Check all lights function correctly
• Inspect tyres for tread depth and damage
• Look for rust holes in the exhaust system
• Verify that the registration plate is visible and secure

Interior inspection:

• Test the horn
• Check all dashboard warning lights illuminate when you turn on the ignition
• Verify that the handbrake holds the vehicle securely
• Test all seatbelts for proper function
• Ensure the fuel cap seals properly

Under the bonnet:

• Check brake fluid level (should be between MIN and MAX marks)
• Verify engine oil level
• Inspect visible hoses for cracks or leaks

Road test:

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• Feel for soft or spongy brakes
• Listen for unusual noises from the suspension
• Check that steering feels responsive

If you identify any issues during this inspection, you have time to address them before your MOT appointment. Many problems are inexpensive to fix.

How to Spot Advisories vs Major Defects

Understanding the difference between advisory items and major defects helps you prioritise repairs.

An advisory is something to monitor. Your vehicle passes the MOT, but the item needs attention soon. Examples include worn brake pads that are still legal thickness or a minor oil leak. You should address advisories within a few months to prevent them from becoming major defects.

A major defect prevents your vehicle from passing. Examples include brake pads below legal thickness, emissions exceeding limits, or a cracked windscreen in the driver's line of sight. Major defects must be repaired before your vehicle can be retested.

A dangerous defect means your vehicle cannot be driven on public roads. Examples include complete brake failure, a severely damaged windscreen that obscures the driver's vision, or a steering system that doesn't respond. Your vehicle will be marked as unfit to drive.

Electric Vehicle MOT Requirements

Electric vehicles have unique MOT requirements because they lack traditional engines and exhaust systems. However, they're tested for the same roadworthiness standards as petrol and diesel cars.

Battery safety is critical. The MOT test checks that high-voltage cables and connectors are properly insulated and not damaged. Thermal management systems must function correctly; if the battery cooling system is faulty, the vehicle fails.

Electric motor systems are checked for proper function. The regenerative braking system must work correctly. The suspension, steering, brakes, and lighting systems are tested identically to petrol vehicles. The main difference is that emissions testing is replaced with electrical system checks.

If you own an electric vehicle in Kettering, Kettering Motorist Centre has specialist expertise in EV diagnostics and servicing. For more information about electric vehicle maintenance and MOT preparation, visit our sister site for electric vehicle specialists.

The 10-Day Rule Explained

The 10-day rule is often misunderstood. If you book your MOT within 10 days of your current certificate expiring, you can take your test early. Your new certificate will be dated from when your old one expires, not from when you take the test. This means you don't lose any MOT validity by testing early.

For example, if your MOT expires on 15 August and you book a test on 10 August, your new certificate will be valid from 15 August, not from 10 August. This rule helps busy vehicle owners book tests in advance without losing validity.

However, if you test more than 10 days before your certificate expires, your new certificate will be dated from the day you take the test. You'll lose the remaining validity from your old certificate.

Book your MOT within 10 days of expiry to maximise your certificate validity.

DIY Pre-MOT Checks vs Professional Inspection

Deciding between DIY pre-MOT checks and professional inspection depends on your confidence and the complexity of your vehicle.

DIY checks work well for:

• Tyre tread depth measurement
• Brake light and indicator functionality
• Windscreen wiper condition
• Visible damage assessment
• Fluid levels

Professional inspection is essential for:

• Brake system performance (requires specialist equipment)
• Suspension wear measurement
• Emissions testing
• Steering system play measurement
• Headlight alignment
• Battery condition (for electric vehicles)

Many vehicle owners perform basic DIY checks, then book a professional pre-MOT inspection if they identify potential issues. At Kettering Motorist Centre, we offer professional pre-MOT inspections using specialist diagnostic equipment. This service identifies potential failures before your official test, giving you time to arrange repairs. Visit our MOT booking page to arrange your pre-test inspection.

How to Avoid MOT Failure

Prevention is far more cost-effective than remediation. A structured maintenance routine eliminates most MOT failures.

Monthly checks:

• Tyre pressure and visual condition
• All lights and indicators
• Brake fluid level
• Engine oil level
• Windscreen washer fluid

Quarterly checks:

• Brake pad thickness
• Suspension for obvious wear
• Steering responsiveness
• Handbrake function
• Wiper blade condition

Annual checks (before MOT):

• Professional brake system inspection
• Suspension system evaluation
• Emissions test (if concerned)
• Headlight alignment verification
• Exhaust system inspection
• Battery condition (electric vehicles)

Addressing minor issues immediately prevents them from becoming major defects. Vehicle age matters. Older vehicles accumulate wear across multiple systems. If your car is over ten years old, consider a professional pre-MOT inspection.

Keep maintenance records. If you perform repairs yourself or use an independent garage, document the work. This demonstrates that your vehicle has been properly maintained and helps identify patterns of wear or recurring issues.

Your MOT test is fundamentally about roadworthiness and safety. Understanding what the test checks and maintaining your vehicle accordingly makes the process straightforward. Most failures are preventable with basic maintenance and attention to common problem areas.

If you're in Kettering or Northamptonshire and want expert guidance before your MOT, Kettering Motorist Centre offers professional pre-test inspections and specialist diagnostic services. Our team has extensive experience identifying potential failures and advising on repairs. Book your MOT appointment online, and our transparent pricing means no surprises.