Around one in three vehicles fail their MOT each year in the UK. That sounds alarming, but here's the thing — a huge proportion of those failures are for issues that could have been spotted and fixed before the car ever reached the testing station.
Knowing what testers look for, and doing a quick check yourself beforehand, can save you the cost and inconvenience of a failure, a retest, and potentially being left without a car. Here are the ten most common MOT failure categories and what you can do about each one.
1. Lights and signalling
This is the single biggest cause of MOT failures, year after year. It covers headlights, tail lights, brake lights, indicators, fog lights, number plate lights, and hazard warning lights.
What testers check
- Every bulb must work
- Headlight aim must be within specification
- Lenses must not be cracked, damaged, or discoloured enough to affect the beam pattern
- Indicators must flash at the correct rate (too fast usually means a bulb is blown)
How to check before the test
Turn on the ignition and walk around the car. Check headlights on dipped and main beam, both indicators, front and rear fog lights, and the number plate light. For brake lights, ask someone to press the pedal while you look, or reverse close to a wall and check for the red reflection.
Replacing a blown bulb costs a few pounds and takes minutes. It's the simplest MOT fix there is.
2. Tyres
Tyre failures cover insufficient tread depth, damage, incorrect size, and mismatched tyres on the same axle.
What testers check
- Tread depth must be at least 1.6mm across the central three-quarters of the tyre, around the entire circumference
- No cuts, bulges, or exposed cord
- Tyres must be the correct size for the vehicle
- Tyres on the same axle should be the same size and type
How to check before the test
Use the 20p test: insert a 20p coin into the main tread grooves. If you can see the outer band of the coin, the tread is likely below 1.6mm and the tyre needs replacing. Also inspect the sidewalls for bulges, cracks, or damage. Check all four tyres — including the inner edges, which wear faster on vehicles with alignment issues.
3. Brakes
Brake failures include worn pads and discs, seized or binding calipers, corroded brake lines, imbalanced braking, and insufficient braking force.
What testers check
- Brake efficiency on a rolling road or decelerometer
- Even braking between left and right sides
- Condition of discs, pads, drums, and shoes
- Brake fluid level and condition of pipes and hoses
- Handbrake operation and efficiency
How to check before the test
Listen for grinding or squealing when braking — this usually means pads are worn. Feel for pulling to one side, which suggests uneven braking. Check that the handbrake holds the car on a slope and isn't travelling too far up. Visually inspect the discs through the wheel spokes for deep scoring or a lip at the edge.
Brake repairs are not a DIY job for most people, but spotting a problem early lets you get it fixed before the test rather than after a failure.
4. Suspension
Worn suspension components are a major failure category, particularly on older vehicles and those that cover high mileage on poor roads.
What testers check
- Shock absorbers for leaks and effectiveness
- Springs for cracks or breaks
- Bushes for excessive wear or deterioration
- Ball joints and track rod ends for play
- Anti-roll bar links and mountings
How to check before the test
Push down firmly on each corner of the car and release. The car should bounce back and settle within one or two oscillations. If it keeps bouncing, the shock absorbers are likely worn. Also listen for clunks or knocks when driving over bumps — this often points to worn bushes or drop links.
5. Driver's view of the road
This category covers the windscreen, wipers, washers, and mirrors — anything that affects the driver's ability to see clearly.
What testers check
- Windscreen damage in the driver's critical viewing area (a zone 290mm wide centred on the steering wheel)
- Wiper blades for wear, splits, or missing rubber
- Windscreen washer operation and fluid level
- Condition and presence of required mirrors
How to check before the test
Look at your windscreen from both inside and outside. A chip smaller than 10mm in the swept area outside the critical zone won't cause a failure, but anything larger than 10mm in the critical zone will. Replace worn wiper blades — they cost under £15 and take two minutes to fit. Top up the washer fluid.
6. Exhaust and emissions
Emission failures are particularly common on older diesel vehicles, though petrol cars with failing catalytic converters also get caught.
What testers check
- Exhaust gas emissions against the vehicle's registered standard
- Exhaust system for leaks (including manifold, pipes, and silencer)
- Catalytic converter presence and condition
- Diesel particulate filter (DPF) condition and presence
How to check before the test
If your engine management light is on, get it diagnosed — it often indicates an emissions-related fault. Excessive smoke from the exhaust (black for diesels, blue for oil burning) is a warning sign. Take the car for a good 20-minute motorway run before the test to clear the DPF and get the catalytic converter up to operating temperature.
You can check whether your vehicle is likely to meet ULEZ emission standards for an indication of its general emissions health. Our guide on Euro emission standards explains which standard your car needs to meet.
7. Steering
Steering failures include excessive play in the steering rack, worn track rod ends, power steering fluid leaks, and damaged steering column components.
What testers check
- Free play at the steering wheel (before the road wheels start to move)
- Condition of track rod ends, ball joints, and steering rack gaiters
- Power steering operation and fluid leaks
- Steering column and universal joints
How to check before the test
With the engine running and the car stationary, gently rock the steering wheel left and right. There should be very little movement before the front wheels start to respond. Any clunking or knocking sounds suggest worn joints.
8. Bodywork and structure
Corrosion and structural damage can cause failures, especially on older vehicles or those that have been in accidents.
What testers check
- Structural integrity of load-bearing areas (sills, chassis rails, subframes, mounting points)
- Sharp edges that could cause injury to pedestrians
- Security of body panels and bumpers
- Condition of the boot and bonnet latches
How to check before the test
Look underneath the car (or as much as you can see) for rust on the sills, floor panels, and subframe. Check that bumpers are secure and there are no jagged edges on damaged bodywork. Structural corrosion that has weakened a load-bearing component will fail — surface rust alone usually won't.
9. Seatbelts and airbags
Every fitted seatbelt must work correctly. The airbag warning light is also checked.
What testers check
- All seatbelts latch, release, and retract properly
- Webbing is not cut, frayed, or damaged
- Mounting points are secure
- Airbag warning light goes out after the engine start sequence
How to check before the test
Pull each seatbelt out fully, check for twists and fraying, and make sure it clicks securely into the buckle. Start the engine and confirm the airbag light illuminates briefly then goes out. If it stays on, there's a fault that needs diagnosing.
10. Registration plates
A surprisingly common failure — and one of the easiest to avoid.
What testers check
- Plates must be present, secure, clean, and legible
- Characters must be correctly spaced and in the legal font
- Plates must not be obscured by tow bars, bike racks, or dirt
- Rear plate light must illuminate the plate
How to check before the test
Clean both plates and make sure they're securely fixed. Check that no characters are faded, missing, or covered. Illegal fonts, tinted plates, or incorrect spacing will also fail.
Your pre-MOT checklist
Before taking your car in, spend ten minutes on this walk-around:
- All exterior lights working (headlights, indicators, brake lights, fog lights, number plate light)
- Tyres above 1.6mm tread, no damage, correctly matched per axle
- Windscreen free of significant chips or cracks in the critical zone
- Wiper blades in good condition, washer fluid topped up
- Mirrors present and undamaged
- Seatbelts latching and retracting properly
- Horn working
- Registration plates clean, secure, and legible
- No engine warning lights illuminated on the dashboard
- Handbrake holding firmly
This won't guarantee a pass, but it will eliminate the most common — and most preventable — failures.
Know your car's history
Before the test, it's worth checking your vehicle's MOT history to see what came up at previous tests. Advisories from last year often become failures this year if they haven't been addressed. Recurring issues — like a suspension advisory that's appeared three years running — are a strong sign that the component is close to failing.
To make sure you always test within the optimal window, set up a free MOT reminder and you'll get an email alert 28 days and 7 days before your MOT expires.
And if your car does need work before the test, Compare MOT prices on BookMyGarage to find competitive garages in your area.
The bottom line
Most MOT failures are preventable. The top ten failure categories — lights, tyres, brakes, suspension, windscreen, emissions, steering, bodywork, seatbelts, and registration plates — account for the vast majority of fails, and many of them can be spotted with a simple walk-around before the test. Spend ten minutes checking the basics, review your previous MOT history for recurring advisories, and book your test with time to spare. A little preparation goes a long way toward a first-time pass.