Failing an MOT is rarely about a mysterious mechanical fault. Year after year, the same five areas dominate failures — lights and signalling, suspension, brakes, tyres, and visibility (windscreen, wipers and the driver’s view of the road). The encouraging part: almost everything on that list can be checked on your own driveway in about ten minutes, with no tools and no mechanical knowledge. A blown bulb costs a few pounds; wiper blades cost £10–£20. Yet these are exactly the things that turn a routine test into a failure and a retest fee. Below are the eight most common failure areas — what the tester looks for, how to check it yourself, typical fix costs, and fail versus advisory.
Advisories vs Failures: What the Tester Grades
Not every problem means a failure. Faults are graded: an advisory means the car passes but the tester has noted wear needing future attention; a minor defect also passes but should be repaired soon; a major defect is an automatic fail; a dangerous defect is a fail and the car must not be driven until repaired. Good pre-MOT checks stop this year’s advisories becoming next year’s major defects.
1. Lighting and Signalling Problems
Faulty lights are among the top reasons cars fail — and the cheapest to fix. Every required lamp must work, show the correct colour, be securely fitted, and (for headlights) be aimed correctly.
How to check at home
Have someone work the controls while you walk around, or use a shop-window reflection at night. Check headlights (dipped and main), sidelights, indicators on all four corners plus side repeaters, hazards, brake lights including the high-level light, reversing light, rear fog light, and number plate lights. Check lenses too — clouded, cracked or water-filled units can fail even with a working bulb.
Cost and fail vs advisory
A bulb costs a few pounds and takes minutes to fit — the classic avoidable failure. Badly aimed headlights fail too, though many centres adjust aim on the spot. A cracked lens is more likely a fail than an advisory.
2. Tyres: Tread, Condition and Damage
Tyres are the only thing connecting your car to the road: 1.6mm of tread across the central three-quarters, all the way round, with no cuts, bulges, exposed cords or serious cracking, and the correct size and type.
How to check at home
Use the 20p test — push a 20p coin into the main grooves at several points; if the outer band shows, tread is below the limit. Check sidewalls for cuts and bulges, look for uneven wear (often a suspension or alignment sign), and check pressures against the handbook or door-sticker figures.
Cost and fail vs advisory
A budget tyre is £60–£100 fitted; a puncture repair around £20. Tread below 1.6mm or a sidewall bulge is a straight fail. Light perishing with legal tread may be an advisory.
3. Brakes and Brake Components
Brakes are measured on the rolling road: effort, left-right balance, handbrake efficiency, and the condition of discs, pads, pipes and hoses. You cannot replicate that, but you can catch the warning signs.
What you can check yourself
Listen for squealing or grinding, feel for pulling to one side or a spongy pedal, and test the handbrake on a slope — it must hold the car still. Do not dismantle brakes yourself; have a mechanic inspect any suspicion. One free check: with the ignition on, no brake, ABS or stability light should stay lit.
Cost and fail vs advisory
Pads near the limit may earn an advisory. Scored discs, a leaking pipe or a handbrake that cannot hold the car are fails — a fluid leak can be dangerous. Expect £100–£200 per axle for pads; corroded pipes commonly fail cars over eight years old.
4. Suspension Problems
Suspension keeps tyres in contact with the road. The tester looks for worn bushes, leaking shock absorbers, broken springs and play in joints and bearings.
How to spot trouble at home
Push down firmly on each corner and release — the car should settle without bouncing on. Listen for knocking over bumps, check the car sits level (one low corner suggests a broken spring), and look at your tyres: uneven wear is often the first visible sign of suspension trouble.
Cost and fail vs advisory
Slight misting on a shock absorber may be an advisory; a leaking shock or broken spring is a fail. Replacement shocks typically cost £150–£300 fitted — book two weeks ahead, not two days.
5. Windscreen, Wipers and Washers: the Driver’s View
The tester judges one thing: can the driver see clearly? Damage over 10mm in the driver’s line of sight fails, as does damage over 40mm elsewhere in the swept area. Wipers must clear effectively and washers must work — an empty bottle leaving washers inoperative is a fail.
How to check at home
Inspect the glass inside and out within the wiper-swept area. A small chip outside it is usually an advisory; anything in the sight line is judged strictly. Run wipers with washers — blades should sweep cleanly — and top up the screenwash. Remove obstructions: oversized stickers, dangling ornaments, a phone mount in the swept area.
Cost and fail vs advisory
Blades cost £10–£20 a pair and take minutes to change. Chip repair is often free via insurance windscreen cover; a full replacement runs into the hundreds, so repair chips before they spread.
6. Number Plates and Bodywork
Plates must be legible, securely fixed, correctly formatted (right font, spacing and grouping) and lit at night. Bodywork only fails where it is a safety issue — sharp edges or corrosion in structural areas.
How to check at home
Wash both plates and read them from a few metres back, by day and with lights on at night. Confirm the plate lights work. Walk round looking for sharp edges — a cracked bumper or bent panel — and serious rust around sills, subframes and suspension mountings on older cars.
Cost and fail vs advisory
Replacement plates cost £20–£30 a pair. An unreadable, cracked or incorrectly spaced plate is a straight fail — and entirely avoidable.
7. Mirrors
Every required mirror must be present, securely mounted and usable — a separate check from the windscreen, confirming you can see behind and alongside the car.
How to check at home
Check the interior mirror and both door mirrors: none missing, loose, or so cracked or discoloured as to be unusable. Adjust each one and confirm the housing holds position rather than flopping about.
Cost and fail vs advisory
Replacement mirror glass typically costs £10–£30 and often clips in without tools. A missing or insecure mirror is a fail; a tiny edge chip may be treated leniently, but do not rely on it.
8. Warning Lights and Dashboard Issues
With the ignition on, every required warning lamp must light up then go out. A lamp staying on is a fail — engine management (it affects emissions), ABS, airbag/SRS, brakes, stability control, and on newer cars driver-assistance warnings.
How to check at home
Switch the ignition on without starting and watch the sequence, then start up and confirm none remain lit. If one does, get a diagnostic check — many garages read codes for £30–£60, and some faults are just a failed sensor.
Cost and fail vs advisory
Little middle ground here: a lit malfunction lamp is a fail, not an advisory. A sensor can be under £100 fitted; emissions faults cost more. A warning light never fixes itself — diagnose it early.
What About Electric Vehicles?
EVs skip the emissions test but fail on exactly the same basics above, plus high-voltage cable condition and labelling, the charging port, and the AVAS low-speed warning sound. See our electric vehicle MOT test guide for the full EV-specific checks.
Your Pre-MOT DIY Checklist
Run through this a few days before your appointment — about 20 minutes:
Lights
- Headlights (dipped and main), sidelights, indicators, hazards, brake lights and rear fog light all work
- Number plate lights work; lenses clean and undamaged
Tyres and visibility
- Tread passes the 20p test on every tyre; no cuts, bulges or cords; pressures correct
- Windscreen clean with no significant damage in the swept area; wipers clear cleanly; screenwash filled
- All mirrors present, secure and usable; nothing obstructing the driver’s view
Brakes, suspension and general
- No grinding, squealing or pulling when braking; handbrake holds on a slope; no warning lights
- No suspension knocks; car sits level; plates clean and legible; horn works; seatbelts latch and retract
Preparation Timeline: One to Two Weeks Before
Do not leave everything until the day before — a bulb is a ten-minute job, but tyres, brakes, suspension and diagnostics need booking in. Work to this timeline:
- Two weeks before: run a free MOT history check — past advisories are a to-do list from previous testers. Book the test now; you can test up to a month (minus a day) before expiry without losing time.
- One week before: do the full DIY checklist. Order parts (bulbs, blades, screenwash) and book garage time for anything beyond DIY.
- A few days before: fit parts, top up fluids, clean plates and lights, and take a short drive listening for anything new.
- Test day: arrive with at least a quarter tank, leave the locking wheel nut key in the car, and keep seatbelts and footwells accessible.
What the Test and a Retest Cost
The maximum Class 4 car MOT fee is £54.85, frozen since 2010. Retest rules are set by law: free if the car stays at the station and is retested within 10 working days; up to half the fee if taken away but returned to the same station within 10 working days; a full fee after 10 working days or at a different station. For your full rights after a failure, read our guide to what happens if your car fails its MOT.
Check Your MOT History Before the Test
A full MOT history check shows every past test — results, mileage readings and every advisory ever recorded. Fix this year’s version of last year’s advisory before the tester finds it. Our pillar MOT guide puts the whole test in context.
Frequently Asked Questions
What are the most common MOT failures?
Lights, suspension, brakes, tyres and visibility — mostly simple faults you can check at home. See GOV.UK’s MOT guidance.
Will my car fail on last year’s advisory?
Not automatically — an advisory means the car passed. But advisories describe wear heading toward the failure threshold, so fix them beforehand.
Can I drive my car if it fails?
Only to a pre-booked repair or retest — and never if a fault is classed as dangerous. You may keep driving if your existing certificate is still valid and no fault is dangerous.
How much does a retest cost?
Free if the car stays at the station and is retested within 10 working days; up to half the fee if taken away but returned to the same station within 10 working days; a full fee after 10 working days or at a different station.
Do electric cars fail MOTs?
Yes. EVs skip emissions but are checked identically on the basics, plus high-voltage systems, the charging port and the AVAS warning sound — see our EV MOT guide.
How early should I start preparing?
One to two weeks before: check the car’s history, run the DIY checklist, order parts, and book garage time for anything beyond a simple fix.
Conclusion
Most MOT failures are not bad luck — they are small, visible, fixable problems that were there weeks before test day. Twenty minutes with the checklist above, a look at your car’s MOT history, and a one-to-two-week preparation window will catch the vast majority. Pair this guide with our 10 MOT check tips, fix the cheap things yourself, book the bigger things early, and you will walk into the test centre with the odds firmly in your favour.