The beam pattern doesn't fall where it should when measured on a headlamp aligner. Too high dazzles oncoming traffic; too low means you can't see far enough ahead. Either way it's assessed against a fixed pattern, not by eye.
Wording as it commonly appears on an MOT certificate: “Headlamp aim beam image projected incorrectly”.
What does it mean?
The beam pattern doesn't fall where it should when measured on a headlamp aligner. Too high dazzles oncoming traffic; too low means you can't see far enough ahead. Either way it's assessed against a fixed pattern, not by eye.
How serious is it?
Usually recorded as: Major. The tester assesses the actual vehicle on the day, so your certificate is what counts.
What normally causes it?
- The manual levelling dial inside the car left on a load setting
- A new headlamp unit fitted and never set up
- Front-end knock, even a minor one, moving the unit
- Sagging or corroded headlamp adjusters on an older car
- Aftermarket LED bulbs in a reflector housing designed for halogen, which scatters the beam
What a mechanic would check
First thing is to check the levelling dial is on zero, because that catches out a surprising number of cars. Then it's on the beam setter and adjusted properly. If someone's fitted LED bulbs to a halogen reflector, no amount of adjusting will produce a correct pattern.
What might need replacing
- Adjustment only, in most cases
- A headlamp unit if the adjusters have broken
- Correct-spec bulbs refitted
Can you still drive it?
It's a failure. Adjustment is usually quick and cheap, and it's worth doing properly on a beam setter rather than against a garage wall.
Repair cost
Setting the aim is a short job at most garages. It only gets expensive if the adjuster mechanism inside the lamp has snapped, which means a new unit.
Before the retest
Walk round the car with someone working the switches: dipped, main, sidelights, indicators, hazards, brake lights including the high-level light, rear fog and number plate lamps. A new headlamp bulb or unit should be followed by a beam aim check, because a correctly working lamp aimed into oncoming traffic still fails. Wipe lenses clean and make sure no warning lights stay on after start-up.
Retest rules
If the vehicle stays at the test centre for repair and is retested within 10 working days, a partial retest is often free; some items qualify for a free retest if you bring the car back by the end of the next working day. The exact conditions are set out on GOV.UK, so confirm with the test centre before you leave. A major or dangerous failure means the car cannot legally be driven away unless the previous MOT is still valid and nothing dangerous was recorded — check your certificate first.
Related help
More lights failures · MOT failure decoder · Ask a mechanic about your certificate
This is general guidance from a UK mechanic, not a substitute for a physical inspection. Only the tester who inspected your vehicle can confirm what was recorded and why.