Price ranking · every failure item
The most expensive things to fail an MOT
The test itself is capped at £54.85. What it can find is not — and the dearest item on the list costs twenty-seven times the fee that uncovered it.
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The most expensive things to fail an MOT are the emissions items: a catalytic converter or a diesel particulate filter reaches £1,500 fitted, against £180 to £460 for brakes and £10 to £25 for a number plate bulb. The dearest failure of all has no price at all — structural corrosion, where the bill depends entirely on what is found once the underseal comes off.
£1,500
the dearest priceable MOT failure — a catalytic converter or a particulate filter, fitted
27×
the multiple between that repair and the £54.85 legal maximum for the test that found it
£8
the cheapest thing on the list — a wiper blade, which fails the same test as the £1,500 one
Every MOT failure item, ranked by what it costs
One certificate, one word — fail — and a bill that ranges across two orders of magnitude. This is every repair that follows a failure, ordered by the top of its price range at an independent garage.
| What failed | The repair | Cost fitted | Test section |
|---|---|---|---|
| Structural corrosion | Cut out and weld, extent unknown until stripped | No honest range | 6.1 |
| Emissions — petrol | Catalytic converter, genuine OEM part | £500 – £1,500 | 8 |
| Emissions — diesel | Particulate filter replaced | £500 – £1,500 | 8 |
| Suspension, all corners | Shock absorbers, all four | £290 – £940 | 5.3 |
| Emissions — diesel | EGR valve replaced | £250 – £750 | 8 |
| Emissions — petrol | Catalytic converter, type-approved aftermarket | £250 – £700 | 8 |
| Exhaust, major leak | Full cat-back system | £300 – £650 | 6 |
| Shock absorber leaking | Shock absorbers, front pair | £160 – £520 | 5.3 |
| Brakes below limit | Pads and discs, one axle | £180 – £460 | 1 |
| Emissions — diesel | Particulate filter cleaned off the car | £250 – £450 | 8 |
| Spring fractured | Coil springs, pair on one axle | £150 – £450 | 5.3 |
| Brake imbalance | Caliper replaced, rear | £170 – £380 | 1 |
| Play in a joint | Lower arm or wishbone, one side | £120 – £320 | 5.3 |
| Exhaust, mid section | Mid section replaced | £140 – £320 | 6 |
| Spring fractured | Coil spring, one front corner | £130 – £320 | 5.3 |
| Excessive bearing play | Wheel bearing, one wheel | £120 – £300 | 5.1 |
| Exhaust, back box | Rear silencer replaced | £90 – £220 | 6 |
| Ball joint play | Ball joint, one side | £70 – £160 | 5.3 |
| Link play | Anti-roll bar drop links, pair | £60 – £150 | 5.3 |
| Exhaust, flexi blowing | Flexi pipe cut out and welded | £60 – £150 | 6 |
| Bush perished | Anti-roll bar bushes | £50 – £130 | 5.3 |
| Tread below 1.6mm | One tyre, common size, fitted | £60 – £120 | 5.2 |
| Beam pointing wrong | Headlamp aim adjusted | £20 – £40 | 4 |
| Plate lamp out | Bulb replaced | £10 – £25 | 4 |
| Blade smearing | Wiper blade replaced | £8 – £25 | 3 |
Independent garage prices, parts and labour, from our own cost guides. Ordered by the top of each range — ordering by the midpoint moves several rows, so the choice is stated rather than hidden. Section numbers are from the DVSA MOT inspection manual. Main dealers charge roughly 50% more on every line here except the tyre. These are estimates; final quotes come from garages.
The expensive end is emissions, which almost nobody expects
Ask a driver what an expensive MOT failure looks like and they will say brakes, or suspension. Both are wrong. The four dearest priceable items on the list are all emissions work: a catalytic converter, a particulate filter, an EGR valve, a full exhaust system. A cat and a DPF each top out at £1,500 — more than pads, discs, a wheel bearing and a set of tyres put together.
The reason is the parts, not the labour. A converter’s cost is the precious metals inside the shell, with fitting only £100 to £250 of the total. That is also why a scrapped cat is worth stealing, and why a type-approved aftermarket unit at £250 to £700 passes the same emissions test as an OEM part at up to £1,500. The test does not award points for the badge on the casing.
And the expensive conclusion is often the wrong one. The most common trigger for condemning a converter, fault code P0420, is frequently a tired £80 to £200 lambda sensor with a perfectly healthy cat behind it. On the diesel side, a blocked filter usually wants a forced regeneration at £75 to £150 or an off-car clean at £250 to £450 long before it wants replacing. **Exhaust the cheap causes first — the retest does not care which one fixed it.**
The dearest failure of all has no price
Corrosion inside a prescribed area is the only item here we refuse to put a number against. Not because we lack the data, but because no number would be honest. Rust within 30cm of a suspension, steering, brake or seatbelt mounting is judged on whether strength or continuity is significantly reduced — and nobody, tester included, knows how far it has spread until the underseal is off and a hammer has been at it.
It can be an hour of welding, or it can be more than the car is worth. The same certificate wording covers a patch the size of a hand and a sill that has quietly stopped being a sill. This is the one failure where a quote given over the phone is worth nothing, and where a second opinion before any cutting starts is worth a great deal.
It is also the item drivers act on fastest, and the numbers show it. Three-quarters of structural corrosion advisories are dealt with before the next test — the highest repair rate of any category in the national record, and far above the 44% for suspension. People do not gamble on rust. The full picture on which advisories get ignored puts that in context.
A turbocharger at £650 to £1,800 and a clutch with a dual-mass flywheel are among the most expensive things that can go wrong with a car, and neither appears anywhere in this ranking. The test never opens the engine and never touches the drivetrain, so neither is inspected. Our guide to what the MOT actually checks covers that boundary properly.
The sideways case is worth knowing, though. A failing turbo can produce visible smoke that fails the emissions test, and an illuminated engine management light is an automatic failure in its own right — so an untested component can still end your test. The same is true of glow plugs at £80 to £200: never tested, but the white smoke they cause on a cold morning can be.
Where the test looks hardest is not where it hurts most
The MOT does not distribute its attention evenly, and the pattern runs opposite to the money.
| Section of the test | Items recorded | Dearest repair in that section |
|---|---|---|
| Axles, wheels, tyres, suspension | 304.9m | £290 – £940 |
| Brakes | 158.7m | £180 – £460 |
| Lamps and electrical | 46.6m | £20 – £40 |
| Emissions and nuisance | 32.7m | £500 – £1,500 |
| Body and structure | 30.5m | No honest range |
| Steering | 13.6m | £70 – £160 |
| Visibility | 12.1m | £8 – £25 |
Items recorded is the count of inspection items logged in the national test record for each section — it measures where the test looks, not how often that section fails. We do not publish a failure rate by section, because the analysis behind it is not finished and a rate without its sample is not a rate.
Suspension and tyres account for nearly ten times as many recorded items as emissions — and the worst they can cost you is a set of four dampers. Emissions is one of the least-inspected sections on the list and holds both of the £1,500 lines. The parts a tester spends the most time on are, on the whole, the affordable ones.
What a failure costs beyond the repair
The repair is the bill you see. There are two more you might not. The first is the retest: leave the car at the same centre and it is normally free, take it away and bring it back within ten working days and it is free or up to half the fee depending on what was fixed, and go past that window or to a different garage and you pay in full again. The detail is in our MOT cost guide.
The second is being off the road. A car that fails on a dangerous defect must not be driven away at all, and one whose certificate has already expired cannot legally be driven except to a pre-booked test or to a garage for repair. On the expensive end of this table — a cat, a filter, structural welding — that is not an afternoon, it is days, and it is the part of an MOT failure that nobody budgets for.
Which is the argument for testing early. You can test up to a month minus a day before expiry and keep your renewal date, so a failure inside that window is an inconvenience rather than an emergency. Test on the last day and the same failure takes your car off the road while you find the money for it.
Most of the list is cheap, and that is the real shape of it
Of the twenty-four priceable repairs here, more than half top out under £330. The headline numbers are real but rare; the everyday experience of failing an MOT is a bulb, a blade, a tyre or a pair of links.
Under £50
Wiper blades, number plate bulbs, headlamp aim, an exhaust rubber mount. Every one of these is a full MOT failure, and every one is cheaper than the test that found it.
Worth checking yourself before you book£50 to £330
Bushes, drop links, ball joints, one tyre, one wheel bearing, a back box, a single spring. The middle of the table and the bulk of real-world failures.
One visit, usually same dayAbove £330
Emissions work, a full exhaust, all four dampers, pads and discs on an axle. Fewer failures land here, but they are the ones worth a second quote before you agree.
Get the figure checked firstHalf the value in this table is knowing which band your failure sits in before you speak to anyone. Our quote checker tells you where a figure sits against typical ranges for your model.
Enter your reg — we’ll read your MOT history, show what testers have already flagged and price each of these repairs for your model rather than the national average.
How this ranking was built
Method
What is ranked. Repairs that follow an MOT failure, ordered by the top of their price range at an independent garage. Only items the MOT actually inspects are included — components outside the test’s scope are excluded even where they are more expensive, and are discussed separately rather than ranked.
Where the prices come from. Our own repair cost guides, which are built from independent-garage parts and labour pricing across the UK and quoted here unchanged. Twelve guides feed this table; each row links to the one it came from so you can check the figure and the workings behind it.
Why the top of the range. Ordering by the midpoint produces a different sequence, because ranges here vary in width from £17 to £1,000. We chose the ceiling because the question the page answers is how bad it can get. Both figures are shown on every row so you can order it the other way if you prefer.
Test sections. Taken from the DVSA MOT inspection manual for cars and passenger vehicles, which applies in England, Scotland and Wales. Northern Ireland runs a separate system under the DVA, so neither the sections nor the fee cap apply there.
What is deliberately not here. No claim about how often each item fails. That needs the reason-for-rejection distribution from the national test record, an analysis we have not completed, and we do not publish a rate without the sample behind it. The items recorded column above counts inspection items logged, which is a measure of attention rather than of failure.
Known limitations. Ranges are national and do not adjust for model, age or region — the same job on a BMW 3 Series sits near the top of every range and a Toyota Yaris near the bottom. Corrosion in a prescribed area is shown without a range because no honest one exists. Prices are estimates; only a garage that has seen the car can quote.
Expensive MOT failures — FAQ
What is the most expensive thing to fail an MOT?
Structural corrosion, because it has no upper limit — the bill depends on how far the rust has spread once the underseal comes off, and it can exceed the value of the car. Of the failures that can be priced, a catalytic converter or a diesel particulate filter is the dearest at £500 to £1,500 fitted.
How much does an average MOT failure cost to fix?
There is no useful average, because the range runs from £8 for a wiper blade to four figures for emissions work, and the two are not remotely equally likely. More than half the repairs on this list top out under £330, so the typical experience is a small bill — but the tail is long enough that an average would mislead in both directions.
Why are emissions repairs the most expensive MOT failures?
Because the cost is in the part rather than the work. A catalytic converter’s price is the precious metals inside it, with fitting only £100 to £250 of the total. A diesel particulate filter is the same story. Very little labour, a very expensive component.
Can a turbo or a clutch fail an MOT?
Not directly — the test never opens the engine and never inspects the drivetrain, so neither is examined. A failing turbo can still end your test sideways, because visible smoke fails the emissions check and an engine management light on is an automatic failure. A worn clutch will never appear on a certificate at all.
Do I have to pay for a retest if my car fails?
Often not. Leave the car at the test centre for the repair and the retest is normally free. Take it away and return it to the same centre within ten working days and it is free for the listed partial-retest items or up to half the fee for anything else. Beyond that window, or at a different garage, you pay the full fee again.
Can I drive my car away if it fails the MOT?
Only if the previous certificate is still valid and no dangerous defect was recorded. A dangerous grading means the car must not be driven at all. If the old certificate has expired, the only legal journeys are to a pre-booked test or to a garage for repair work that has been arranged.
Is a corroded exhaust an MOT failure?
Not on its own — corroded but not leaking is an advisory. The failure comes with a major leak, an insecure system or excessive noise. Repairs run from £60 to £150 for a flexi pipe welded in, through £90 to £220 for a back box, up to £300 to £650 for a full cat-back system.
Is it cheaper to fix things before the MOT?
For the small items, almost always — a blade, a bulb or a headlamp adjustment costs the same whenever you do it, but doing it first avoids a failure on the record and a return trip. For the expensive items, the answer is the opposite: do not pre-emptively replace a converter or a filter on suspicion. Get the fault diagnosed first.
Should I always replace a catalytic converter if it fails emissions?
No, and this is the single most expensive mistake on this page. The common trigger, fault code P0420, is often a tired lambda sensor at £80 to £200 rather than the converter itself. Where the converter genuinely has failed, a type-approved aftermarket unit at £250 to £700 passes the same test as a genuine part at up to £1,500.
How do I find out what my car is likely to fail on?
Your own MOT history is the best predictor there is, because testers record advisories that name the component a year or more before it becomes a failure. Our advisory decoder reads that history from your registration and puts a price for your model next to every item on it.
The guides behind these numbers
Every price in the table comes from one of these. Each shows the parts, the labour hours and the model-by-model spread behind its range.