The 10 Most Common MOT Failures (And How to Fix Them for Under £20)
Around 28% of cars fail their MOT each year. The most common failures are lighting and signalling (24% of failures), brakes (21%), suspension (18%) and tyres (12%). The good news: most are cheap, easy fixes — a blown bulb, a worn wiper blade, or low screenwash — that you can sort yourself for under £20 before the test.
The 10 Most Common MOT Failures (And How to Fix Them for Under £20)
Every year, roughly 28% of cars fail their MOT test in the UK. That's more than 7 million vehicles sent away with a failure notice — and the frustrating part? The vast majority of those failures are caused by cheap, easy-to-fix problems that any motorist could have sorted beforehand.
We've dug into the latest DVSA (Driver and Vehicle Standards Agency) data to bring you the most common MOT failure categories, what actually goes wrong, and — crucially — how you can fix most of them yourself for under twenty quid.
Let's get into it.
1. Lighting and Signalling — 24% of Failures
The single biggest reason cars fail the MOT. Nearly a quarter of all failures come down to lights that aren't working properly.
What the tester checks
- All headlamps (dipped and main beam)
- Sidelights and tail lights
- Brake lights
- Indicators (including side repeaters)
- Fog lights (rear is mandatory if fitted; front if fitted)
- Number plate lights
- Headlamp aim
What usually goes wrong
In most cases, it's simply a blown bulb. A single dead indicator bulb or a dodgy brake light is enough to fail the test outright. Headlamp aim being slightly off is another common one — this can happen if you've changed a bulb and not refitted it properly, or if the adjuster mechanism has worn.
Can you fix it yourself?
Absolutely. Replacing a bulb is one of the simplest car maintenance jobs there is. On most cars, you can access the headlamp and tail light bulbs from inside the engine bay or boot without any tools at all — just twist, pull, swap, and refit.
What you need
- Spare bulb kit — covers headlamps, indicators, sidelights, brake lights, and tail lights. A universal kit costs around £5–£8.
- Headlamp alignment — if you suspect the aim is off, most garages will adjust it for a few quid. You can also check it yourself against a flat wall.
Cost to fix: £3–£10
CarOkay tip: Our Essential Kit includes a full spare bulb kit that covers every common bulb type. Keep one in the boot year-round — it's handy for more than just MOT prep.
2. Brakes — 21% of Failures
The second most common failure, and one of the most safety-critical areas the tester examines.
What the tester checks
- Brake pads and discs (condition and thickness)
- Brake fluid level and condition
- Handbrake operation and efficiency
- Brake pipes and hoses (for corrosion, leaks, and damage)
- Brake pedal condition (rubber, travel, firmness)
- ABS warning light (must not be illuminated)
What usually goes wrong
Worn brake pads are the most frequent culprit. If your pads are below the minimum thickness (1.5mm), you'll fail. Corroded or seized brake components are common on older cars, especially those that don't do many miles. Brake fluid contamination is another sneaky one — the fluid absorbs moisture over time, which reduces its effectiveness.
Can you fix it yourself?
Partially. Checking brake fluid level is straightforward — just look at the reservoir under the bonnet. Testing brake fluid quality requires a simple electronic tester (dip it in, read the result). Changing brake pads is within the ability of a confident DIYer, but if you're not sure, leave it to a mechanic.
What you need
- Brake fluid tester — around £8–£12. Tells you instantly whether your fluid needs changing.
- Brake pads — vary by vehicle, typically £10–£30 for a set.
- Visual inspection — look through the wheel spokes at the disc and pad. If the disc has a pronounced lip around the edge, or you can't see much pad material left, get it checked.
Cost to fix: £0 (if just fluid top-up) to £30+ (new pads)
CarOkay tip: Our Ultimate Kit includes a brake fluid tester — a quick dip test can save you a failed MOT and a return trip to the garage.
3. Suspension — 18% of Failures
Worn suspension components account for nearly one in five MOT failures. This one catches people off guard because suspension wear happens gradually — you get used to the ride deteriorating.
What the tester checks
- Shock absorbers (dampers) — for leaks and effectiveness
- Springs — for cracks, breaks, and corrosion
- Ball joints and track rod ends — for excessive play
- Anti-roll bar links and bushes
- Wheel bearings — for roughness and play
- CV joints and gaiters — for splits and damage
What usually goes wrong
Leaking shock absorbers are extremely common, especially on cars over five years old. Broken coil springs are another frequent find — they often snap at the bottom coil where road salt and moisture cause corrosion. Split CV boots are a classic MOT failure: the rubber gaiter splits, grease escapes, dirt gets in, and the joint eventually fails.
Can you fix it yourself?
Inspection, yes. Repair, usually not. You can get underneath the car (safely on axle stands or a ramp) and look for obvious leaks, broken springs, and split boots. But replacing suspension components typically requires specialist tools and a wheel alignment afterwards.
What you need
- Visual check — look for oily residue on the shock absorbers, cracked or broken springs, and any split rubber boots on the driveshafts.
- Bounce test — push down firmly on each corner of the car and release. It should bounce back and settle within one or two bounces. If it keeps bouncing, the shock absorbers are likely worn.
Cost to fix: Varies widely — inspection is free, repairs from £30–£200+
CarOkay tip: Suspension is one of those areas where catching it early saves you money. A split CV boot is a £15 fix at a garage; a failed CV joint is £150+.
4. Tyres — 12% of Failures
One in eight cars fails on tyres — and it's almost always avoidable.
What the tester checks
- Tread depth (minimum 1.6mm across the central three-quarters of the tyre, around the full circumference)
- Tyre condition (cuts, bulges, cracks, or exposed cords)
- Tyre size and type (must match on the same axle)
- Tyre pressure (not directly tested, but low pressure can affect other checks)
What usually goes wrong
Insufficient tread depth is the big one. The legal minimum is 1.6mm, but many motoring organisations recommend changing tyres at 3mm. Bulges in the sidewall (caused by impact damage from potholes) are also common and are an instant fail.
Can you fix it yourself?
You can certainly check. A proper tread depth gauge costs pennies and takes seconds to use. The old "20p test" works in a pinch — insert a 20p coin into the tread grooves. If you can see the outer band of the coin, your tread is getting low.
What you need
- Tread depth gauge — around £2–£4. Far more accurate than the coin method.
- Tyre pressure gauge — £5–£10. Correct pressure improves tread wear, fuel economy, and handling.
- New tyres — if needed, budget tyres start from around £40–£60 fitted, depending on size.
Cost to fix: £2 (gauge) to £50+ (per tyre if replacement needed)
CarOkay tip: Our kits include a proper tread depth gauge. Check your tyres monthly, not just before the MOT — it's safer and it saves you money on uneven wear.
5. Visibility — 8% of Failures
Windscreen and wiper issues cause 8% of MOT failures. This one is genuinely easy to sort.
What the tester checks
- Windscreen condition (chips, cracks)
- Windscreen wipers (condition and effectiveness)
- Washer jets (they must produce a clear stream)
- Washer fluid level
- Mirrors (condition and security)
What usually goes wrong
Worn wiper blades are the most common visibility failure. They're one of those things you don't notice getting worse because the deterioration is so gradual. Windscreen chips in the driver's line of sight (Zone A — a 290mm-wide area directly in front of the driver) will fail if they're larger than 10mm. Outside Zone A but within the swept area, the limit is 40mm.
Empty washer fluid is an instant fail — and it's possibly the easiest MOT failure to avoid.
Can you fix it yourself?
Yes, every single one of these. Wiper blades take two minutes to change. Screenwash costs a couple of quid. Even windscreen chips can be repaired with a DIY kit for under a tenner (though professional repair is often covered by insurance).
What you need
- Wiper blades — around £6–£15 for a pair, depending on type and size.
- Screenwash concentrate — £2–£5. Never use plain water — it freezes in winter and doesn't clean properly.
- Windscreen chip repair kit — £8–£12 for a DIY kit, or check your insurance for free professional repair.
Cost to fix: £2–£15
CarOkay tip: Fresh wiper blades and a full screenwash bottle are included in every CarOkay kit. It's the easiest pass you'll ever get.
6. Number Plates — 7% of Failures
Surprising to many, but 7% of MOT failures are down to number plates. It's often overlooked in pre-MOT checks.
What the tester checks
- Plates must be present, secure, and legible
- Correct font, spacing, and format
- No discolouration, damage, or fading that makes characters hard to read
- Number plate light must illuminate the rear plate
- Plates must conform to current regulations (BS AU 145e for plates fitted after September 2021)
What usually goes wrong
Cracked, faded, or dirty number plates are the usual culprits. A plate that's been clipped by a car park bollard, or one that's yellowed and cracked from UV exposure, will fail. Loose plates that are hanging off or secured with cable ties instead of proper fixings can also cause a failure. Non-standard fonts or illegal spacing (like making "AB51 TER" look like "ABSI TER") are an automatic fail.
Can you fix it yourself?
Easily. Clean the plate, check it's securely fixed, and make sure the light behind the rear plate works. If the plate itself is damaged or faded beyond repair, a replacement from a registered supplier costs around £15–£20.
What you need
- Number plate fixings — proper screw and cap kits cost around £2–£3.
- Replacement plates — around £15–£20 for a pair from a registered supplier (you'll need your V5C or other ID).
- Bulb for number plate light — under £2.
Cost to fix: £2–£20
CarOkay tip: Our Premium Kit includes proper number plate fixings. No more cable ties or missing screws.
7. Exhaust and Emissions — 5% of Failures
Exhaust issues account for 5% of failures, covering both the physical exhaust system and the emissions it produces.
What the tester checks
- Exhaust system security and condition (no leaks, holes, or excessive corrosion)
- Emissions levels (CO, HC, and lambda for petrol; smoke opacity for diesel)
- Catalytic converter presence and function
- DPF (Diesel Particulate Filter) — must be present if originally fitted, and functioning
- No visible smoke from the exhaust
What usually goes wrong
For petrol cars, a failing lambda sensor or old spark plugs can push emissions over the limit. For diesels, a clogged DPF is increasingly common — especially on cars that do lots of short trips and never get a good motorway run to regenerate the filter. Corroded exhaust sections, particularly around joints, are common on older vehicles.
Can you fix it yourself?
Some of it. Giving a diesel car a good 30-minute motorway drive before the test can help clear the DPF. DPF cleaning additives added to the fuel tank can also help. Checking for obvious exhaust leaks (listen for blowing noises) is simple. But replacing exhaust sections or sensors is usually a garage job.
What you need
- DPF cleaner additive — around £8–£15. Add to the fuel tank before a long drive.
- Exhaust repair paste/bandage — £5–£10 for temporary fixes on minor leaks.
- New spark plugs — £8–£20 for a set of four (petrol cars). Can improve emissions significantly.
Cost to fix: £5–£20 (DIY), more for major exhaust work
CarOkay tip: Our Ultimate Kit includes DPF cleaner — add it to your fuel tank a week before the test and take the car for a good run.
8. Steering — 3% of Failures
What the tester checks
- Power steering operation and fluid level
- Steering rack condition and security
- Steering column and universal joints
- Steering wheel condition and play
What usually goes wrong
Worn steering rack bushes and track rod ends cause excessive play in the steering. Power steering fluid leaks are also common. The tester will check for excessive free play at the steering wheel — for cars with rack and pinion steering, the limit is around 13mm of movement before the wheels start to turn.
Can you fix it yourself?
Checking is easy; fixing usually isn't. Top up power steering fluid if it's low (around £5 for a bottle). But worn components in the steering system need a mechanic.
Cost to fix: £5 (fluid top-up) to £100+ (component replacement)
9. Bodywork and Structure — 2% of Failures
What the tester checks
- Structural integrity (chassis, subframes, sills, load-bearing areas)
- Sharp edges or projections that could injure pedestrians
- Corrosion that affects the structure
- Doors (must open from inside and outside)
- Seats and seat belts (condition, security, and function)
- Fuel filler cap security
What usually goes wrong
Structural corrosion is the main concern — if rust has weakened a load-bearing part of the body (sills, chassis rails, mounting points), the car will fail. Sharp bodywork edges from accident damage can also cause a failure.
Can you fix it yourself?
Minor surface rust, yes. Treat it with rust converter and protective paint to stop it spreading. But structural corrosion typically requires welding — that's a garage job.
Cost to fix: £5 (rust treatment) to £200+ (welding)
10. Horn — 1% of Failures
The simplest one on the list. Your horn must work. Press it. Does it make a noise? You're sorted.
What the tester checks
- Horn must be present, secure, and audible
- Must produce a continuous, uniform sound
What usually goes wrong
The horn simply doesn't work — usually a blown fuse, a corroded connection, or (rarely) a dead horn unit.
Can you fix it yourself?
Yes. Check the fuse first (your handbook will tell you which one). If the fuse is fine, check the wiring connections at the horn itself. A replacement horn costs about £10–£15.
Cost to fix: £0 (fuse) to £15 (new horn)
The Bottom Line
Here's the thing that gets us at CarOkay: the majority of MOT failures cost under £20 to fix. A blown bulb. Worn wipers. Low screenwash. A dodgy number plate light. These are not expensive problems — they're just overlooked ones.
The average MOT retest costs around £25–£50 depending on the garage, and that's before you factor in the inconvenience of a second trip. A few minutes of checking — and a few quid spent on the right bits — can save you time, money, and hassle.
Quick Reference: Common MOT Failures at a Glance
| Failure Category | % of Failures | Typical DIY Cost | Difficulty |
|---|---|---|---|
| Lighting & signalling | 24% | £3–£10 | Easy |
| Brakes | 21% | £0–£30 | Easy to moderate |
| Suspension | 18% | Inspection free | Moderate to hard |
| Tyres | 12% | £2–£50+ | Easy (check) |
| Visibility | 8% | £2–£15 | Easy |
| Number plates | 7% | £2–£20 | Easy |
| Exhaust & emissions | 5% | £5–£20 | Easy to moderate |
| Steering | 3% | £5–£100+ | Hard |
| Bodywork & structure | 2% | £5–£200+ | Moderate to hard |
| Horn | 1% | £0–£15 | Easy |
What to Do Next
- Run through the checks above a week or two before your MOT is due.
- Fix what you can — bulbs, wipers, screenwash, tyre pressures, number plate fixings.
- Get the right parts in one go — our CarOkay kits are designed to cover the most common failure points in a single box.
- Book with confidence — knowing you've covered the easy stuff means you're far less likely to face a surprise failure.
Good luck with your test. And if you want to make the whole process easier, run a free vehicle health check — it takes 60 seconds and tells you exactly what to look out for.
Good question
Frequently asked questions
What are the most common MOT failures?
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The biggest single cause is lighting and signalling at 24% of failures — usually just a blown bulb. Brakes follow at 21%, suspension at 18%, and tyres at 12%. Visibility issues (wipers, washers, windscreen) cause 8%, and number plates a surprising 7%. Most of these are cheap and avoidable: a bulb, a wiper blade, or topping up screenwash costs only a few pounds and prevents a failed test.
What percentage of cars fail their MOT?
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Roughly 28% of cars fail their MOT first time — more than 7 million vehicles a year in the UK. The frustrating part is that the majority fail on cheap, easily-fixed faults rather than serious mechanical problems. Running through a few basic checks a week or two before your test dramatically improves your chances of a first-time pass.
How can I avoid failing my MOT?
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Check the easy things a week or two before your test: walk around the car checking every bulb works, top up the screenwash, inspect wiper blades, check tyre tread is above 1.6mm with no bulges, and make sure the number plate is clean and secure. Sort any warning lights on the dashboard. Most failures come down to these basics, and fixing them yourself costs under £20.
How much does it cost to fix common MOT failures?
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Most common failures are cheap to fix yourself: a bulb is £3–£10, a pair of wiper blades £6–£15, screenwash £2–£5, and number plate fixings £2–£3. Tyres are the main exception, from around £40–£60 fitted. Compared with a £25–£50 retest fee plus a return trip, spending a few pounds on the basics beforehand almost always pays off.
Will an advisory cause an MOT failure?
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No — an advisory is a warning that something is wearing but is still within legal limits, so the car passes. It is a heads-up that the item, such as brake pads getting low or a tyre nearing the limit, will likely need attention before the next test. Acting on advisories early is cheaper than waiting for them to become outright failures.
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