Common Things That Will Fail An MOT Test

Understanding What Will Fail an MOT

To pass its annual MOT test, your vehicle must meet minimum standards of roadworthiness and environmental compliance. Numerous components and systems are scrutinised, and any significant defect or safety concern will result in a failure. These failures aren't arbitrary; they are based on stringent criteria designed to ensure all vehicles on public roads are safe for their occupants and other road users, and that they meet emissions standards. Knowing the most frequent culprits behind a failed MOT can save you time, money, and stress.

The MOT test aims to ensure your vehicle is safe and environmentally sound. Common things that will fail an MOT include issues with brakes, tyres, lights, steering, suspension, emissions, and body structure. A failure means your vehicle is not legal to drive on the road until the necessary repairs are made and it passes a re-test. Understanding these common failure points allows for proactive maintenance, preventing unexpected issues on test day.

• Brakes, tyres, and lights are frequent MOT failure points.
• Structural integrity and emissions are critical safety and compliance areas.
• A failed MOT requires repairs before the vehicle can be legally driven.
• Proactive checks can prevent unexpected test failures and re-test costs.

The Driver and Vehicle Standards Agency (DVSA) publishes detailed guidance, often referred to as the MOT testing manual, which outlines every single item tested and the precise criteria for passing or failing. For Class 4 vehicles, which covers most cars, the manual specifies exactly what inspectors look for. This document is the definitive source, but it's highly technical. For most vehicle owners, understanding the most common areas where failures occur is far more practical. These are the aspects that most frequently cause vehicles to be deemed unroadworthy.

It’s important to distinguish between a failure and an advisory. An advisory is noted when a component is approaching a condition that could cause it to fail in the near future. While not an immediate failure, advisories should be addressed to prevent future problems and maintain the vehicle's overall safety and condition. Ignoring advisories can lead to a failure at a subsequent MOT. Conversely, a failure means the vehicle is unsafe or illegal *right now* and cannot be used on public roads until fixed.

Many drivers wrongly assume that older cars are exempt from MOTs. While there are specific exemptions, such as for vehicles manufactured before a certain date (currently before 1st January 1961 in the UK), most vehicles over three years old require an annual MOT. The question 'why are old cars MOT exempt' often arises, but the reality is only a very small percentage qualify. For the vast majority, regular testing is a legal requirement.

What is a Fair Test MOT?

A 'fair test MOT' refers to a vehicle inspection conducted honestly and thoroughly by a qualified tester, adhering strictly to the DVSA's guidelines. It means all required checks are performed without bias, and the outcome reflects the vehicle's actual condition against the legal standards. A fair test ensures that components are assessed correctly for safety and compliance, without any undue leniency or excessive strictness that deviates from the official MOT testing manual class 4 requirements.

Tyres: The Rolling Roadblocks to Passing

Tyres are one of the most common reasons for an MOT failure, and for good reason. They are the only point of contact between your vehicle and the road, directly impacting grip, braking, and steering. Inspectors meticulously check several aspects of your tyres, and any deficiency can lead to a fail.

The primary concern is tread depth. The legal minimum tread depth for cars in the UK is 1.6mm across the central three-quarters of the breadth of the tyre, covering its entire circumference. However, inspectors will also look for any cuts, cracks, bulges, or exposed cords on the tyre walls or tread. Damage that compromises the tyre's structural integrity, or even the risk of it doing so, will result in a failure. This includes severe cracking, blistering, or any sign that the tyre is nearing its end of life and could burst.

Tyre Condition Checks

Beyond tread depth and visible damage, the MOT test also examines:

• Uneven Wear: Excessive or uneven wear patterns can indicate underlying problems with wheel alignment, suspension, or tyre inflation. While sometimes noted as an advisory, severe uneven wear that compromises safety will fail the vehicle.
• Correct Type: Tyres must be the correct type and size for the vehicle as specified by the manufacturer. Mixing tyre types (e.g., radial and cross-ply) on the same axle is prohibited.
• Inflation: While not directly tested for pressure, tyres must not be significantly under or over-inflated to the point where it causes safety issues.
• Re-grooved Tyres: Tyres that have been re-grooved are illegal for passenger vehicles and will result in an MOT failure.

It is crucial to regularly inspect your tyres yourself. Check tread depth using a tread depth gauge or a 20p coin (if the outer band is visible when inserted, the tread is below 1.6mm). Look for any signs of damage or bulges on the sidewalls. Ensuring your tyres are properly inflated also contributes to even wear and safety.

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A windscreen mot failure can also occur due to tyre issues, particularly if tyre debris has been thrown up and damaged the screen. However, the primary checks for tyres themselves focus on their direct road-worthiness.

Lighting and Signalling: Be Seen and Be Understood

Visibility is paramount for road safety. The MOT test rigorously checks all the lights on your vehicle to ensure they function correctly and are aimed appropriately. A faulty light is not just a nuisance; it can lead to accidents by preventing you from seeing the road or other drivers from seeing you, or by giving incorrect signals.

Every light fitted to the vehicle must be tested, from headlights and taillights to brake lights, indicators, and even the number plate light. The colour of the light emitted is also crucial; for instance, headlights must emit white light, and rear lights red light. Any light that is not working, is obscured by dirt or damage, or emits the wrong colour will cause an MOT failure.

Common Lighting Failures

Inspectors look for:

• Headlights: Both dipped and main beam must work. They must also be correctly aimed. If headlights are too high, they can dazzle oncoming drivers; too low, and they won't illuminate the road sufficiently. Misaligned headlights are a common reason for failure.
• Taillights: Must emit red light and be visible.
• Brake Lights: All brake lights must illuminate when the pedal is pressed. This includes any centrally mounted third brake light.
• Indicators (Turn Signals): Front, rear, and side indicators must flash amber and be clearly visible. They must flash at the correct rate.
• Hazard Lights: Must operate correctly, flashing all indicators simultaneously.
• Number Plate Light: This must be present and working, illuminating the rear number plate with white light.
• Reflectors: Rear reflectors must be present and in good condition.

The condition of the lenses is also important. If they are cracked, opaque, or heavily faded, they can obscure the light or change its colour, leading to a failure. For example, yellowed or clouded headlight lenses significantly reduce light output and can cause a fail. Ensuring all bulbs are correctly rated and fitted is also part of this inspection. A dodgy mot test might overlook a minor bulb issue, but a thorough inspection will catch it.

Braking System Defects: Stopping Power is Non-Negotiable

The braking system is arguably the most critical safety component on any vehicle. Its ability to stop the car effectively and safely under various conditions is paramount. Any compromise in the braking system's performance or integrity will result in an immediate MOT failure.

The MOT test assesses the brakes thoroughly, checking not only their performance but also the condition of all associated components. This includes the brake pedal, master cylinder, brake pipes and hoses, callipers, discs, drums, and pads. Even minor issues can lead to a failure if they indicate a potential safety risk or a significant reduction in braking efficiency.

Key Braking System Checks

Inspectors will check for:

• Brake Performance: This is measured using a brake roller tester. It measures the braking force applied by each wheel and compares it to the vehicle's weight. There are specific minimum braking force requirements for service and parking brakes.
• Brake Fluid: While the fluid level itself isn't always a direct fail, if it's contaminated or the reservoir is empty, it indicates a significant problem and will fail.
• Brake Pipes and Hoses: These must be free from corrosion, leaks, or damage. Corroded pipes or perished, kinked, or chafing hoses are serious safety concerns.
• Brake Discs and Pads: Discs must not be excessively worn, scored, or cracked. Pads must have sufficient material remaining; there's a minimum thickness requirement. Cracked discs or pads worn down to the metal backing plate are immediate fails.
• Callipers and Cylinders: Must not be leaking fluid. Seized or binding callipers can also cause issues.
• Parking Brake: Must hold the vehicle securely on a gradient.

The MOT testing manual class 4 details the exact percentage of efficiency required for the service brake and parking brake. If your brakes feel spongy, pull to one side when braking, make grinding noises, or the warning light is on, these are all strong indicators of potential MOT failure points. A fair test mot will expose any deficiencies here.

Steering and Suspension: Maintaining Control

The steering and suspension systems work together to ensure your vehicle is controllable, stable, and comfortable to drive. Defects in either system can significantly compromise handling, making it difficult to steer accurately or maintain stability, especially at higher speeds or during evasive manoeuvres.

The MOT test scrutinises various components within these systems for wear, damage, or signs of imminent failure. Loose or worn parts in the steering or suspension can lead to unpredictable vehicle behaviour, making them critical safety items. A vehicle that drifts excessively, feels unstable, or has excessive play in the steering wheel is likely to fail.

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Steering System Checks

Inspectors will examine:

• Steering Wheel Play: Excessive free movement in the steering wheel before the wheels begin to turn indicates wear in the steering rack, column, or linkages.
• Steering Linkages: Ball joints, track rod ends, and other connecting components must be free from excessive wear, damage, or looseness.
• Steering Rack/Box: The main steering mechanism must not be leaking fluid or show signs of excessive wear or damage.
• Power Steering: If the vehicle has power steering, the system must be functioning correctly, and there should be no fluid leaks.

Suspension System Checks

Suspension components checked include:

• Shock Absorbers: Must not be leaking fluid or be excessively corroded. Their damping ability is also assessed.
• Coil Springs: Should not be cracked, fractured, or weakened.
• Suspension Arms and Mountings: Bushings must not be perished, cracked, or missing. Bearings must be free from excessive play.
• Wheel Bearings: Must be properly adjusted and free from excessive play.

Any component that is loose, excessively worn, or damaged and could affect the vehicle's control or stability will cause an MOT failure. The mot testing manual class 4 provides detailed specifications for wear limits on these parts. For instance, if a shock absorber is leaking significantly or a suspension arm mounting is loose, it's an immediate fail.

Exhaust Emissions and Engine Management

Environmental regulations are a significant part of the MOT test, focusing on the emissions produced by your vehicle's engine. A vehicle that pollutes excessively or has a faulty engine management system will fail. This aspect ensures that vehicles comply with current air quality standards.

The emissions test measures the levels of various pollutants in the exhaust gases. The specific limits vary depending on the age and type of vehicle, with older vehicles often having slightly more lenient standards. However, any readings above the prescribed limits, or any fault codes logged by the engine management system that relate to emissions control, will lead to a failure.

Emissions Test Details

The test typically involves:

• Diesel Particulate Filter (DPF): For diesel vehicles, the presence and functionality of the DPF are checked. A missing or deliberately removed DPF will cause an MOT failure.
• Exhaust Gas Analysis: A probe is inserted into the exhaust pipe to measure pollutants like carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and particulates.
• Visible Smoke: For diesel vehicles, excessive visible smoke is a failure point.

Beyond emissions, the engine management system is also checked. If the Malfunction Indicator Lamp (MIL), often known as the 'check engine' light, is illuminated on the dashboard, the vehicle will fail the MOT. This light indicates a fault detected by the vehicle's onboard diagnostic (OBD) system, which could affect emissions or engine performance.

A dodgy mot test might overlook a slightly high reading, but a proper inspection uses calibrated equipment to provide an accurate assessment. Ensuring your engine is well-maintained, the exhaust system is sound, and the DPF is functioning correctly (if applicable) is vital for passing this section of the test. This also includes ensuring the catalytic converter is present and functioning correctly for petrol vehicles.

Body, Structure, and Other Critical Areas

The MOT test extends beyond mechanical components to assess the structural integrity and safety of the vehicle's bodywork. Significant corrosion or damage to the chassis, frame, or body panels can compromise the vehicle's overall strength and safety, leading to a failure.

This part of the test focuses on areas that could affect the vehicle's structural integrity or pose a hazard to occupants or other road users. It includes checking for sharp edges, protruding parts, or weakness in critical load-bearing areas. The MOT testing manual class 4 provides detailed guidance on what constitutes a structural defect.

Key Body and Structural Checks

Inspectors will examine:

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• Chassis and Frame: Must be free from excessive corrosion or damage that could weaken the structure.
• Body Panels: Excessive corrosion or damage that creates sharp edges, compromises structural integrity, or affects the mounting of other components will fail.
• Doors: Must open and close correctly from the inside and outside, and the latches must work properly.
• Seatbelts: All seatbelts must be present, correctly anchored, and function properly, locking when pulled sharply. They must not be frayed or excessively worn.
• Seats: Driver's seat must be adjustable.
• Windscreen: Damage within a specific area directly in the driver's line of sight will cause a windscreen mot failure. Chips or cracks larger than 10mm in the driver's direct view, or larger than 40mm elsewhere in the swept area, will fail.
• Wipers and Washers: Must effectively clear the windscreen.
• Horn: Must be operational and audible.
• Fuel System: Fuel lines and tank must be secure and free from leaks.
• Battery: Must be securely mounted.

While not every minor scratch or dent results in an MOT failure, any issue that affects structural integrity, safety, or the proper functioning of essential safety equipment like seatbelts or the windscreen will lead to a fail. Regular checks of your vehicle's bodywork, especially for rust on sills, wheel arches, and the chassis, can preemptively identify potential problems.

Can You Drive a SORN Car to MOT Without Insurance?

The rules surrounding driving a vehicle to its MOT test are specific and must be adhered to. If your vehicle is declared SORN (Statutory Off Road Notification), it is not legally allowed on public roads. This means you cannot simply drive it to an MOT test centre under normal circumstances. Driving a SORN vehicle on the road is illegal and carries penalties.

However, there is a specific exemption. You *can* drive a vehicle that is declared SORN to and from a pre-booked MOT test appointment. This is the only permitted time a SORN vehicle can be used on public roads. It is crucial that the appointment is pre-booked. You cannot drive it for any other purpose, such as running errands or visiting a garage for repairs unrelated to the MOT preparation.

Insurance Requirements

The question, 'Can you drive a SORN car to MOT without insurance?', brings up another critical point. While the SORN status allows you to drive to a pre-booked MOT, standard UK law requires all vehicles used on public roads to have at least basic third-party insurance. The exemption for driving to an MOT appointment does *not* exempt you from the insurance requirement. Therefore, you must have valid insurance covering you for the journey to and from the MOT test centre, even if the vehicle is SORN.

The only exception to this is if you are driving directly from the MOT test centre to a pre-booked repair appointment, or directly from a repair appointment to home, if the vehicle has just passed its MOT. In all other scenarios, a SORN vehicle requires insurance if it is to be driven on a public road, even for the sole purpose of attending an MOT.

A dodgy mot test scenario might involve someone trying to drive an untaxed, uninsured vehicle to an MOT, which is illegal. Always ensure your vehicle is correctly declared and insured for any journey on public roads.

What to Do If Your Car Fails its MOT

Receiving news that your car has failed its MOT can be disheartening, but it's important to remember that it's a necessary safety check. The immediate consequence of a failure is that your vehicle is no longer legally permitted to be driven on public roads until the necessary repairs are completed and it passes a re-test. However, there are clear steps to follow.

Firstly, the MOT test centre must provide you with a 'Refusal of an MOT Test Certificate' (VT30) form. This document lists all the reasons why your vehicle failed. It's essential to keep this form, as it details exactly what needs to be repaired. The test centre should also explain the issues clearly and provide an estimate for the repairs if you choose to have them done by them.

Re-testing Options

You have a few options for getting your vehicle repaired and re-tested:

• Repair at the Test Centre: If the repairs are minor, they may be able to fix them on-site and perform a partial re-test. For most failures, this involves a re-test of the failed items.
• Repair Elsewhere: You can take your vehicle to another garage or repair it yourself.
• Partial Re-test: If you leave the test centre for repairs, you can bring the vehicle back for a partial re-test. This is often free if the vehicle is re-tested within one working day of the original failure, and the repairs are minor (e.g., fixing lights, replacing a tyre). If you take the car away, the rules for re-testing apply. A full MOT fee may apply if the vehicle is re-tested more than one working day later, or if it is a major failure requiring a full re-test.

It is illegal to drive a vehicle that has failed its MOT on public roads unless you are driving it to a pre-booked MOT appointment or to a place of repair. You can, however, drive it to a pre-booked MOT test if it is still within its valid MOT certificate period but is due for a re-test after failing. If your existing MOT has expired, you can only drive it to a pre-booked test or repair.

The aa mot test, or any reputable test centre, will provide clear documentation. If you are unsure about the repairs or the cost, it is advisable to get a second opinion or quote before authorising work. Understanding 'when is 1st mot due on a new car' can help you plan ahead for future tests, but dealing with a failure requires prompt action.