Cracked Headlight Repair: What Lasts and What Passes the MOT
Cracked headlight repair comes in three forms: clear tape, a resin kit, or a new lens bonded to the original unit. The first two buy time; only the third puts back the seal that keeps water off the bulbs, boards and reflector. Here is how each holds up, and how a cracked lens is treated at the MOT.
Why a small crack matters
The clear lens is more than a cover. It is bonded to the housing all the way round, and that bond keeps spray, grit and road salt away from everything inside.
A crack, even a short one from a stone thrown up on the motorway, breaks the barrier. Damp air gets in, the lens mists, and over a winter the reflector and any LED boards start to suffer.
Some lenses also craze from the inside, a web of fine lines that no polish can reach. It is a known trait of some SEAT Leon lenses.
Repair tape and resin kits: how long they hold
- Clear headlight repair tape is quick and cheap, and fine for getting home or to the next garage. Heat from the lamp, rain and the car wash lift its edges in time.
- Resin or crack-filler kits fill the surface of the crack and can stop it spreading. They seldom reach all the way through, so the seal stays open underneath.
- Restoration and polishing kits deal with haze on the surface. They do nothing for a crack that goes through the lens.
Any of these can see you through to a proper repair. None of them seals the lamp again, and the MOT has a view on what you stick over the beam.
Cracked lenses and the MOT
Section 4.1 of the MOT inspection manual grades the headlamp lens and reflector. Slightly defective is a minor defect; seriously defective or missing is a major one. A car with only minor defects passes, while any major defect is a fail.
Testers are also told to assess damaged or repaired lamps for security, colour, light output and durability. A hairline crack that leaves the beam untouched is a different case from a broken lens with water behind it, and the grading is the tester's judgement.
Tape counts too. A product on the lens that obviously reduces the light, or changes its colour to anything other than white or yellow, is listed as a major defect.
When the damage goes past the lens
Look behind the lens first. If the crack runs into the black housing, or a mounting tab has snapped, a new lens alone will not do.
A housing that is split, holed or broken in two is replaced, and the internal parts move across to the new one. Snapped tabs can take a repair kit or a new housing, and the MOT lists a lamp not securely attached as a major defect. Both are covered under Headlight Repair Services.
A new lens on the original unit
The repair that lasts is a new lens. The unit comes off the car, the old lens is separated from the housing, the old sealant is cleared and the new lens is bonded on and left to cure before testing.
Bulbs, LED boards, projector and reflector stay as they are, so the beam pattern and the match with the other side do not change. A new lens stays clear for years, where a polished one tends to cloud again within months.
The work is set out in full on Headlight Lens Repair and Replacement.
Questions about cracked headlights
Can a cracked headlight lens be fixed without replacing it?
A crack can be filled or taped, which slows it down, but the original seal stays broken. To make the lamp watertight again the lens is replaced and the unit resealed.
Will a cracked headlight fail the MOT?
It depends on how bad it is. A slightly defective lens is a minor defect and still passes; a seriously defective or missing lens is a major defect and fails.
Is tape over the crack allowed at the MOT?
Tape that obviously cuts the light or changes its colour is a major defect. Clear tape that leaves the beam alone is not caught by that line, though the tester still judges the lens underneath.
Got a cracked lens?
Send photos of the crack and of the lamp switched on, with the car's details. The price for a new lens comes back before you post anything, and the headlight travels to us by courier within the UK, or is collected where that can be arranged.
Send the details, get a price back
Say which car it is and what the headlight is doing, add a couple of photos, and your quote arrives by email. Nothing has to come off the car until you have agreed to it.