Will a faulty adjuster fail an MOT?

Yes if the beam aim is out of specification and cannot be adjusted, or if the dipped beam shifts during a tap test. The tester checks beam aim against marked tolerances.

Can I adjust headlights at home?

Rough adjustment is possible by aiming at a marked wall at a measured distance, but final aim should be set with proper beamsetter equipment to comply with MOT and traffic regulations.

Why does my adjuster motor whine but not move?

Stripped internal gear — the motor spins but loses drive to the actuator screw. The motor is usually serviceable separately if the gears are available, otherwise replace the adjuster as a unit.

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Headlight Adjust Screw buying guide — what to know before you buy

The headlight adjustment screw or motor sets the vertical and horizontal beam angle. Manual adjusters use a screw and gear mechanism; electric versions integrate a small motor controlled by a dashboard switch or automatic levelling system. A faulty adjuster prevents correct beam aim and is an MOT failure.

When to replace

Replacement is needed when the beam aim is impossible to set within tolerance or the adjuster physically fails. Beam aim is checked at every MOT.

Beam aim out of specification at the MOT and not adjustable
Adjuster gear strips when the screw is turned
Electric adjuster motor whines but does not move the reflector
Headlight bumps audibly when the levelling switch is operated
Visibly broken screw or motor housing on the back of the headlight

What to look for when buying

Adjusters are specific to the headlight model. Some can be replaced separately; others require buying the complete headlight unit.

Confirm whether the adjuster is serviceable separately on your headlight
Manual screw vs electric motor — different part numbers
Auto-levelling vehicles use a position sensor on the suspension that pairs with the motor
Many aftermarket adjusters fit OEM and replacement headlights interchangeably
Replacement may require partial disassembly of the headlight unit

Common failure modes

Adjusters are exposed to heat, vibration, and water. Plastic gears and electric motors are the typical failure points.

Stripped plastic gear inside the adjuster body
Electric motor brushes worn out from frequent levelling cycles
Internal corrosion from water leaking past a damaged headlight seal
Position sensor drift on auto-levelling systems
Cracked adjuster housing from stone strike

Related parts to check together

The beam-aim system involves several parts. Check the surrounding components when an adjuster fails.

Headlight unit — inspect for moisture ingress and lens clarity
Headlight adjustment motor — distinct from the manual screw on auto-levelling cars
Headlight washer nozzle — check operation if the vehicle has automatic levelling and washer system
Suspension level sensor — provides input for auto-levelling on lowered vehicles