MOT advisories explained

MOT certificates use terse wording from the inspection manual. Here is what the most common advisories and defects mean in plain English, roughly how urgent each one is, and what to ask about. These are general notes, not advice about a specific car.

Last reviewed 22 October 2026.

How urgent is it?

Fix now

Dangerous or illegal to drive with. Sort it before using the car.

Fix soon

Will get worse and may fail the next MOT. Budget for it in the next few months.

Keep an eye on it

Normal wear or minor. Check it at the next service.

For information

Not a fault in itself, but worth knowing.

The words on the certificate

Nearside

the passenger side of the car in the UK (the kerb side, left as you sit in it)

Offside

the driver’s side in the UK (right as you sit in it)

Advisory

not a fail; something the tester thinks will need attention

Minor

a defect with no significant effect on safety; the car still passes

Major

a fail; may affect safety or the environment

Dangerous

a fail; the car must not be driven until it is fixed

Numbers in brackets

the section of the MOT inspection manual the defect falls under, e.g. (5.2.3 (e))

Common advisories and defects

• Tyre damaged to the cords or bulging Fix now

  The tyre’s structure is damaged and it can burst without warning. It is illegal to drive on and must be replaced.

• Tyre close to the legal tread limit Fix soon

  The tread is wearing down towards the 1.6 mm legal minimum, or wearing unevenly on one edge. Uneven wear often means the wheel alignment or suspension needs checking too. Expect to replace the tyre within a few months. More on this advisory

• Tyre rubber cracking with age Keep an eye on it

  Old rubber is cracking on the surface. It is not an immediate fail, but tyres over about six years old lose grip and should be replaced even with plenty of tread left.

• Brake pads wearing thin Fix soon

  Brake pads are consumable; this one is near the end of its life. Replace soon or they will score the discs and the job gets more expensive. Below 1.5 mm it is a fail. More on this advisory

• Brake discs worn or scored Keep an eye on it

  Discs wear with the pads and show surface pitting or a lip at the edge. Usually they are replaced together with the next set of pads. "Not seriously weakened" means they are still safe for now. More on this advisory

• Brake pipes corroding Fix soon

  Metal brake lines rust from the outside in. "Slightly corroded" is common on older cars and is an advisory; "excessively corroded" is a fail because the pipe can split and you lose braking. Get it looked at. More on this advisory

• Brakes not working evenly Fix soon

  One side brakes harder than the other, or the braking effort fluctuates. Causes range from a sticking caliper to a warped disc. It affects stopping in a straight line and tends to get worse.

• Corrosion on the body or underbody Keep an eye on it

  "Corroded but not seriously weakened" means rust is present but the structure is still sound. On older cars this is routine, but it only goes one way: once rust reaches a prescribed area or weakens a mounting it becomes a fail, and welding is costly. Check how far it has spread. More on this advisory

• Oil leak Keep an eye on it

  The engine or gearbox is weeping oil. "Not excessive" means it is not dripping onto the road, which would be a fail. Common culprits are gaskets and seals. Keep the oil level topped up and ask a garage where it is coming from. More on this advisory

• Shock absorber starting to leak Keep an eye on it

  Light misting of oil on a shock absorber is early wear. A heavy leak, or a shock that no longer damps the suspension, is a fail. Shock absorbers are usually replaced in pairs across an axle. More on this advisory

• Wear in a suspension or steering joint Fix soon

  A joint or rubber bush has slight play or wear. It can cause knocking noises, vague steering and uneven tyre wear, and it becomes a fail once the movement is "excessive". Not an emergency but worth fixing before the next test. More on this advisory

• Protective rubber cover split or missing Fix soon

  The rubber boot that keeps dirt out of a joint has failed. Cheap to replace on its own; left alone, dirt destroys the joint behind it and the repair gets expensive.

• Suspension spring corroded or damaged Fix soon

  Corroded springs can snap, often when hitting a pothole, which can puncture a tyre or leave the car sitting unevenly. A fractured spring is a fail. More on this advisory

• Exhaust leaking or loose Fix soon

  A small leak is noisy and slowly gets worse as the pipe rusts through. A major leak is a fail and can let fumes into the cabin. Repairs range from a clamp to a new section.

• Exhaust emissions too high Fix soon

  The engine is producing more pollutants than allowed. Causes include a tired catalytic converter, a faulty sensor or a poorly running engine. Sometimes a service and a long run fixes it; sometimes it needs a new catalyst.

• Diesel particulate filter problem Fix now

  The DPF traps soot. "Tampered with" or "removed" means it has been illegally modified, which is a fail and can bring a fine. A blocked DPF is an expensive repair; ask for evidence of what was done.

• Engine warning light on Fix soon

  The car’s computer has logged a fault. Since 2018 a lit engine management light is a major fail. The fault could be trivial or serious; a diagnostic scan will say which.

• Headlights pointing too high or low Fix soon

  The beam is out of alignment, dazzling other drivers or lighting too little road. Usually a quick adjustment at a garage. It is a fail at the test itself but most testers adjust and retest on the spot. More on this advisory

• A light not working Fix now

  A bulb or its wiring has failed. Cheap to fix, but driving with a lamp out is illegal and a fail.

• Light lens damaged or faded Keep an eye on it

  A cracked or faded lens lets water in and dims the light. It becomes a fail when the lamp no longer shows the right colour or is insecure.

• Wiper or washer not clearing properly Keep an eye on it

  Worn wiper blades or a weak washer jet. Blades are a cheap fix and a fail if they cannot clear the screen.

• Windscreen chipped or cracked Keep an eye on it

  Damage outside the driver’s direct view is an advisory if it is under 40 mm. In the driver’s line of sight anything over 10 mm is a fail. Chips can often be repaired cheaply before they spread.

• Battery loose or leaking Fix soon

  The battery is not clamped down properly. A loose battery can short against the bodywork. Usually fixed in minutes.

• Seat belt wear or damage Fix now

  A frayed, cut or slow-retracting belt may not hold you in a crash. Any damage to the webbing or a buckle that does not latch is a fail.

• Odometer could not be read or looked tampered with For information

  The tester could not take a reliable mileage reading. There is no reading for this test in the history, which makes the mileage timeline harder to trust. Ask for service records.

• Steering wear or leak Fix soon

  Play or a leak in the steering system. It makes the car vague to drive and becomes a fail once movement is excessive or power steering fluid is leaking badly.

• Number plate or its lamp Keep an eye on it

  A damaged, faded or badly lit plate. Cheap to fix; a plate that cannot be read is a fail.

• Fuel system leak or faulty cap Fix now

  Fuel leaks are a fire risk and a fail. A fuel cap that does not seal lets fumes out and is also a fail.

• Horn not working properly Fix soon

  The horn is weak, intermittent or not working. Usually a cheap fix. A horn that does not work is a fail.

Want to see the advisories on a specific car? Run the free check.