Headlight Failures: Common MOT Pitfalls

The MOT test is a crucial annual check designed to ensure your vehicle is safe and roadworthy. While many drivers focus on brakes, tyres, and emissions, a surprisingly common reason for a vehicle to fail its MOT is due to issues with the headlights. These aren't just about illumination; they're about correct alignment, intensity, and functionality, all of which are vital for safe driving, especially during the darker months. Understanding why your headlights might be failing is the first step to ensuring a successful MOT and, more importantly, your safety on the road.

The Importance of Headlights in the MOT Test

Your headlights are fundamental safety features. They allow you to see the road ahead and, crucially, make your vehicle visible to other road users. The MOT test rigorously checks several aspects of your headlights to ensure they meet legal standards. These checks are not arbitrary; they are based on regulations designed to prevent accidents caused by poor visibility or dazzling other drivers.

Common Reasons for Headlight Failure

Several factors can lead to your headlights failing the MOT. Let's break down the most frequent culprits:

1. Incorrect Aim or Alignment

This is arguably the most common reason for headlight failure. Headlights that are aimed too high can dazzle oncoming drivers, creating a dangerous situation. Conversely, headlights aimed too low will not illuminate the road sufficiently, increasing the risk of accidents. During the MOT, testers use specialised equipment to check the dip and height of your headlight beams. Even a slight misalignment can result in a fail.

Factors affecting alignment:

• Vehicle Load: Carrying heavy loads in the boot or with passengers can significantly alter the rear suspension, causing the front of the car to lift and consequently change the headlight aim. Many vehicles have manual headlight levellers to compensate for this, and their incorrect setting can cause a fail.
• Suspension Issues: Worn suspension components can lead to the vehicle sitting lower or higher than intended, affecting beam alignment.
• Accidental Damage: Even minor bumps or impacts can knock the headlights out of alignment.

2. Bulb Issues

While seemingly straightforward, bulb problems are a frequent cause of MOT failure.

• Burned-out bulbs: If a headlight bulb is completely out, it's an immediate fail. This applies to both main beam and dipped beam bulbs.
• Incorrect bulb type: Using bulbs that are not E-marked (European standard) or are of the wrong wattage for your vehicle can also lead to a fail. These bulbs may not provide the correct light output or colour, or they could overheat and damage the headlight housing.
• Dim or weak bulbs: Even if a bulb is still working, if its light output is significantly diminished, it may not meet the required illumination standards.

3. Damaged or Corroded Headlight Units

The physical condition of the headlight unit itself is also assessed.

• Cracked or misted lenses: Cracks in the headlight lens can allow moisture to enter, causing the inside of the unit to mist up. This significantly reduces light output and can cause light to scatter, dazzling other drivers. Misted or yellowed lenses are a common MOT fail.
• Corrosion: Corrosion on the headlight's internal reflectors or electrical connections can impair performance and lead to failure.
• Loose units: Headlight units that are not securely fixed to the vehicle will also result in a fail.

4. Incorrect Colour of Light

The colour of the light emitted by your headlights is strictly regulated.

• Blue or overly white light: While some aftermarket bulbs claim to offer a 'whiter' light, if it's too far towards blue, it can be deemed illegal and cause a fail. The standard colour for dipped and main beam headlights is white.
• Coloured bulbs: Any coloured bulbs (other than the legal amber for indicators) are a definite fail.

5. Inoperative Daytime Running Lights (DRLs)

If your vehicle is fitted with Daytime Running Lights (DRLs) as standard, and they are not functioning correctly, this can also lead to an MOT failure. DRLs are designed to make vehicles more visible during daylight hours.

Legal Requirements and MOT Standards

The MOT test is based on the Road Vehicles Lighting Regulations 1989 (as amended). These regulations specify:

• Number of lights: A vehicle must have at least two working headlights.
• Type of lights: Headlights must be either white or yellow (though white is the most common and legally preferred).
• Beam pattern: The dipped beam must be correctly aimed to avoid dazzling other drivers, and the main beam must provide adequate illumination.
• Light intensity: The light output must be sufficient.

The MOT manual provides specific guidelines for testers, including checks for beam alignment, intensity, and any damage or defects to the headlight units.

Checking Your Headlights Before the MOT

You can perform several checks yourself to minimise the risk of your headlights failing the MOT:

1. Visual Inspection: Walk around your car and check that both headlights are clear of cracks, misting, or significant yellowing. Ensure they are securely fitted.
2. Functionality Test: With the engine running, switch on your dipped headlights, then your main beam headlights. Check that both bulbs in each unit are working. Also, test your fog lights if fitted.
3. Alignment Check (Basic): Park your car on a level surface facing a wall or garage door. With the engine off, turn on your dipped headlights. Observe the pattern of the light on the wall. You should see a distinct cut-off line, with the light slightly higher on the offside (passenger side in the UK) to illuminate the kerb. If the beams appear too high, too low, or uneven, they may need adjusting.
4. Bulb Type: Ensure you are using the correct type and wattage of bulbs as specified in your vehicle's manual.

What to Do if Your Headlights Fail the MOT

If your vehicle fails the MOT due to headlight issues, you will be given a refusal of an MOT test certificate and a statement of failure. You will need to have the necessary repairs carried out. In most cases, you can drive your vehicle away if the existing MOT is still valid, or if the necessary repairs are minor and do not pose an immediate danger to road users. However, it's advisable to get the issues rectified as soon as possible.

Common remedial actions include:

• Headlight Alignment Adjustment: This is usually a quick and inexpensive fix at a garage.
• Bulb Replacement: Replacing burned-out or incorrect bulbs is straightforward.
• Headlight Unit Replacement: If the lenses are cracked, heavily misted, or the unit is damaged, the entire unit may need replacing. This can be more costly, especially for modern vehicles with complex headlight systems (e.g., Xenon or LED units).
• Lens Restoration: For lightly misted or yellowed lenses, a headlight restoration kit or professional cleaning service can sometimes be effective, but heavily damaged or cracked lenses will require replacement.

Can I Fix Headlights Myself?

Simple issues like replacing a bulb or cleaning slightly misty lenses can often be tackled by DIY enthusiasts. However, headlight alignment is a precision task that requires specific equipment and knowledge. Attempting to adjust it without the proper tools can lead to incorrect aiming and potentially cause a fail or even be dangerous. For alignment or significant damage, it's best to entrust the job to a qualified mechanic.

Headlight Types and Their MOT Implications

Modern vehicles often come with different types of headlights, each with specific considerations:

Halogen Headlights

These are the most common type. They use a filament heated by electricity to produce light. Issues are typically bulb failure or misalignment.

Xenon (HID) Headlights

These use an electric arc through xenon gas to create a brighter, whiter light. MOT testers check for correct functioning, absence of flickering, and proper self-levelling systems (if fitted). A failed Xenon bulb or a malfunctioning ballast can lead to an MOT fail.

LED Headlights

Increasingly common, LED headlights are energy-efficient and long-lasting. The MOT checks for the same criteria as Xenon: correct functioning, no flickering, and proper alignment. If an LED unit fails, it often means replacing the entire unit, which can be expensive.

Adaptive/Cornering Headlights

Many newer cars have headlights that adjust their beam pattern or direction based on steering input or speed. These systems are also subject to MOT checks. If the adaptive or cornering function is not working, it can result in a fail.

Table: Common Headlight Defects and MOT Outcomes

Frequently Asked Questions (FAQs)

Q1: My MOT tester said my headlights are too dim. What does that mean?
It means the light output from your bulbs isn't strong enough to meet the required brightness standards for safe driving. This could be due to aging bulbs, a faulty reflector inside the headlight unit, or using bulbs with the wrong specifications.

Q2: Can I legally put brighter bulbs in my car?
You can fit brighter bulbs, but they must be E-marked and the correct type for your vehicle. Extremely high-wattage or non-approved bulbs can cause a fail and may even damage your headlight housing or wiring.

Q3: My headlight lens is slightly yellow. Will it fail the MOT?
If the yellowing is minor and doesn't significantly affect light output or cause scattering, it might pass. However, if it's pronounced and impairs visibility or causes glare, it will likely result in a fail. Restoration kits can help, but if it's severe, replacement may be necessary.

Q4: Does the MOT test check fog lights?
Yes, if your vehicle is fitted with front or rear fog lights, their operation and condition are checked as part of the MOT test.

Q5: How much does it cost to get headlights aligned?
Headlight alignment typically costs between £20 and £50, depending on the garage and your location. It's a relatively quick procedure.

Conclusion

Headlights are a critical component for both your safety and the safety of others on the road. Understanding the common reasons for MOT failure related to your headlights, performing regular checks, and addressing any issues promptly will not only help you pass your MOT with flying colours but also ensure you can drive safely at any time of day or night. Don't underestimate the importance of your headlights – they are your eyes on the road.