MOT advisory explained
“Brake disc worn, pitted or scored, but not seriously weakened”
Your car passed. The tester wrote this because the disc has visible wear that is not bad enough to fail — yet. Here is what each of those three words describes, how long you realistically have, and the point at which it becomes a failure.
The disc still stops the car properly today. But this advisory rarely stays an advisory: worn discs keep wearing, and the phrase “not seriously weakened” is the only thing standing between a pass and a fail.
Plan it within months rather than days, and before your next test. There is no legal deadline and no obligation to act now.
Front axle, fitted. Rear is usually cheaper, and an electronic parking brake adds a little. Main dealers charge roughly 50% more — model-by-model prices in the brake cost guide.
Light scoring can be a trapped stone rather than a worn disc, and a brand-new disc is technically “worn” after one drive. The advisory on its own does not prove you need a full set.
A “brake disc worn, pitted or scored, but not seriously weakened” advisory means the disc has visible corrosion, grooves or thinning that the tester judged short of a failure, so the car passes. Replacing discs and pads costs £180–£460 per axle fitted. Of 35.8 million tracked brake advisories, 9.4% later returned as a failure.
Pitted, scored or worn — three faults, one sentence
This is the most common brake advisory recorded in the UK, and it covers three different things under one phrase. They have different causes and different urgencies — and the tester’s wording does not tell you which one you have.
- Pitting is corrosion. Small craters in the braking surface, caused by moisture sitting on the disc. It is why cars that stand still for weeks develop this advisory faster than cars driven daily, and why the rear discs on a lightly used car often look worse than the fronts despite doing less work. Light pitting polishes off within a few firm stops. Deep pitting does not, because the pad can no longer make full contact.
- Scoring is mechanical. Circular grooves cut into the disc, usually by grit trapped between pad and disc, or by a pad worn so far that its metal backing plate touched the disc. That second cause matters: heavy scoring is often evidence that pads were left too long at some point in the car’s past, and it tends to come with the pads needing replacement anyway.
- Wear is thickness. Every disc loses material over its life, and every disc has a minimum thickness set by the manufacturer. This is the one that decides pass or fail, and it is measured, not eyeballed. It also produces the lip you can feel with a fingernail at the outer edge — the untouched rim showing how much material the pad has removed from the rest.
Why this matters practically: a quote should name which one. Surface pitting on an otherwise thick disc is a different conversation from a disc measured close to its limit, even though the certificate says the same thing about both.
How long you actually have
Legally, until your next MOT. The car passed, no deadline attached, no obligation to repair. Anyone telling you otherwise is selling something.
Practically, it depends on what is left. A disc with plenty of thickness and light surface pitting can run for another year or more without changing much — corrosion tends to stabilise once the car is driven regularly. A disc measured within a millimetre of its minimum is a different case, because the wear rate accelerates as the disc thins and holds less heat.
The pads decide the timing more often than the disc does. Discs and pads are replaced together because fitting new pads to a grooved disc wears the pads out fast and gives poor braking, while fitting a new disc with old pads does the same in reverse. So the realistic answer is usually: whenever the pads are due, which on a typical car means the same visit.
If the advisory appeared alongside a pad advisory on the same certificate, treat that as the timer. If it appeared on its own, ask for the measurement and plan from there.
The point where an advisory becomes a failure
This is what almost nobody explains, and it is the whole reason the advisory wording is so specific. The certificate says “but not seriously weakened”. Remove those five words and you have a major defect and a failed test.
There is no single legal thickness. The MOT inspection manual does not name a figure in millimetres, because the limit belongs to the manufacturer, not the government. It is cast or stamped into the disc itself, usually on the hub face or the outer edge, marked as a minimum thickness. A tester measures against that number. Which means anyone quoting you a universal “discs fail below X millimetres” is guessing.
That makes this the opposite of the pad rule. Brake pads have a published limit — 1.5 mm, the same for every car on the road, printed in the inspection manual. Discs have no such figure. Two items on the same axle, assessed by the same tester, and only one of them can be checked against a number you are able to look up.
Three things turn this advisory into a fail: the disc measuring below the manufacturer’s minimum, corrosion or scoring deep enough that the tester judges the disc significantly weakened, or a crack. The first is objective and measurable. The second is a judgement call made by the person under your car, which is exactly why the same disc can get an advisory at one station and a fail at another.
What this gives you is a fair question rather than an argument: what did it measure, and what is the minimum stamped on it? A garage that has the disc off can answer in seconds. A garage quoting from a service menu cannot.
How often does this advisory become a failure?
This can be measured rather than guessed. Following every brake advisory forward to the same vehicle’s later tests, across 35.8 million of them, shows what actually happened.
| What happened next | Brake parts | Suspension | Tyres |
|---|---|---|---|
| Became a failure at a later test | 9.4% | 18.7% | 9.9% |
| Ignored, no action taken | 36.1% | 37.1% | 30.5% |
| Fixed | 54.4% | 44.2% | 59.6% |
| Median advisory to failure | 376–379 days — the next MOT | ||
From the DVSA MOT testing bulk dataset (Open Government Licence v3.0): 829.7 million tests and 145.1 million advisories tracked to each vehicle’s later tests, from 35,816,965 brake advisories. Defect code 1.1 covers brake components generally, not discs alone.
One in eleven brake advisories comes back as a failure, and roughly a third are never acted on at all. Those are useful figures, but for discs specifically there is a second thing going on inside them, and it is worth understanding before you read the number as a forecast.
Everywhere else on this site, an advisory becoming a failure means the part got worse. For discs that is only half the story. “Not seriously weakened” is a judgement with no published number behind it, so the same disc, in the same condition, can be written up as an advisory by one tester and a failure by the next.
Some of the 9.4% is therefore a disc that deteriorated, and some is a disc that was assessed differently. The national record cannot separate the two, and neither can we — the certificate stores the outcome, not the reasoning. It is the one figure on this site that measures human judgement alongside metal.
Which makes the measurement the only thing you control. A disc checked against the minimum stamped on it turns an opinion into a number — and that number is the same at every station in the country.
What it costs to put right
| Job | Price fitted | Notes |
|---|---|---|
| Discs and pads, front axle | £180–£460 | The usual job — they are replaced together |
| Discs and pads, rear axle | Usually lower | Smaller discs, less work on most cars |
| Skimming instead of replacing | Rarely economic | Labour often exceeds a new pair |
| Electronic parking brake | Adds to labour | Rear calipers must be wound back electronically |
Independent garage prices, parts and labour. Main dealers typically charge around 50% more. Full prices by model on the brake pads and discs cost page.
Small hatchbacks sit at the bottom of the range; premium and rear-wheel-drive cars at the top. The difference between an independent and a main dealer is almost entirely the hourly rate rather than the parts.
Skimming discs is rarely worth it. Machining a disc back to a flat surface is possible and was standard practice when discs were thick and expensive. On modern cars the discs are thinner and cheap enough that skimming removes material you cannot spare, and the labour often costs more than a new pair. If it is offered, ask what the disc measures now and what it would measure afterwards.
One axle, not four wheels. Front and rear wear at different rates and get replaced separately. An advisory on one axle is not a reason to do both, and a quote covering all four corners deserves the question of what the other axle measured.
| Worked example — front axle, mid-size hatchback | |
|---|---|
| Discs, pair, quality aftermarket | £70 |
| Pads, axle set | £45 |
| Labour — 1.5 h × £65 | £98 |
| Typical total | ≈ £215 |
Sits at the lower end of the £180–£460 range, which runs up to premium and larger cars. Prices from the brake pads and discs guide, which has the figure for your model.
Enter your reg — we’ll read your MOT history, decode each advisory and price it for your exact model.
What happens if you leave it
Braking performance falls off gradually rather than suddenly, and mostly in the wet, where a pitted surface has less area making contact. You are unlikely to notice it happening. What you will notice is a pulsing through the pedal if the disc wears unevenly, and a grinding noise if the pads run out and their backing plates meet the disc.
That grinding is the expensive threshold. Once metal has touched metal, the disc is scrap regardless of thickness, and if a caliper was already sticking you may be looking at that too — the caliper guide covers what that adds.
Two other consequences worth knowing. The advisory sits in your car’s public MOT history permanently, so a buyer can see it and see whether you acted on it. And if a worn brake contributed to a collision, an insurer can reasonably ask why an advisory naming that brake was left untouched. Neither is a legal requirement to repair. Both are reasons the record matters.
What to do next
- Ask for the measurement and the stamped minimum. Two numbers, seconds to read with the wheel off, and together they turn a judgement into arithmetic. This is the single most useful question on this page.
- Ask which of the three words applies. Pitting, scoring and thinning have different causes and different urgencies. A quote that repeats the certificate back at you has not answered anything.
- Check whether the pads were flagged too. If they were, that is your timer — the two jobs share the labour, so doing them together costs less than doing them apart.
- Treat one axle as one job. Front and rear wear at different rates. A quote covering all four corners should come with a measurement for each axle, not one advisory applied to the whole car.
Brake disc advisory FAQ
What is the minimum legal thickness for a brake disc?
There isn’t a universal one. The minimum is set by the vehicle manufacturer and cast or stamped into the disc itself, usually on the hub face or outer edge. A tester measures against that figure, which is why nobody can tell you a single number that applies to all cars — and why any quote citing one is guessing.
Is a pitted brake disc dangerous?
Not at the advisory stage. Pitting reduces the contact area between pad and disc, which costs you a little braking performance in the wet rather than creating a sudden risk. It becomes a failure only when the tester judges the disc significantly weakened by the corrosion, or when it measures below the manufacturer’s minimum.
Can a scored brake disc be skimmed instead of replaced?
Sometimes, but rarely economically. Skimming machines the surface flat again, and it was standard when discs were thick and costly. Modern discs are thinner and cheap enough that the material removed matters and the labour often exceeds a new pair. If it is offered, ask what the disc measures before and after.
Do I have to replace both discs on the axle?
In practice yes, and for a good reason: mismatched discs brake unevenly, which pulls the car under braking. Both discs on one axle are replaced together as standard. The other axle is a separate job with its own wear rate, and an advisory on the front is not a reason to do the rear.
Should the pads be changed at the same time?
Almost always. New pads bedding onto a grooved disc wear quickly and brake poorly, and a new disc with old pads does the same in reverse. The labour to reach one is the labour to reach the other, so doing them together costs less than doing them separately.
Will this advisory fail my next MOT?
Only if the disc deteriorates past the limit in the meantime. A thick disc with light surface pitting can pass again; a disc close to its minimum thickness usually cannot. Ask for the measurement rather than guessing — it is the only figure that decides this, and it takes seconds to read.
How often does a brake disc advisory become an MOT failure?
Across 35.8 million tracked brake advisories, 9.4% returned as a failure at a later test, 54.4% were fixed and 36.1% were ignored. For discs, read that figure with care: because “not seriously weakened” is a judgement rather than a published measurement, part of that 9.4% is a disc that deteriorated and part is the same disc assessed differently by another tester. The record cannot separate the two.