MOT advisory explained
“Coil spring corroded”
Your MOT passed, but the tester has flagged rust on a suspension spring. Here’s what that means, how long you’ve got, and why this is the one advisory that gives you no second warning.
Rust has pitted the steel of one of your suspension springs. It is an advisory rather than a failure because the spring is still intact and carrying the load — but corrosion does not reverse, and a corroded spring is a spring on its way to snapping.
The failure point is fracture, and it arrives without notice: no noise, no warning light, no change in how the car drives. Usually on a cold morning, over a pothole.
Per axle pair, fitted. Springs are replaced in pairs — model-by-model prices in the coil spring replacement cost guide.
This is the classic “book it before winter” advisory. The same pair costs the same in July as in December, but in July you choose the garage, the timing and the quote — and you are not also paying for recovery and a ruined tyre.
A “coil spring corroded” advisory means rust has pitted the steel of a suspension spring, but it is still intact and carrying the load, so the car passes. Replacing the pair costs £130–£320 fitted. Of 27 million tracked suspension advisories, 18.7% later returned as a failure.
What the tester actually saw
A coil spring is a steel bar wound into a helix and held under permanent tension — it carries the weight of your car at that corner, every second, whether you’re driving or parked. Springs sit low in the wheel arch, where road salt, spray and grit collect and stay. Over years, that salt pits the protective coating and then the steel itself.
What the tester is looking at is surface scaling and flaking, usually on the lower coils where debris settles. They’re judging whether the corrosion has gone beyond cosmetic — whether the steel section is visibly reduced. If it has but the spring is intact, that’s an advisory. If it’s fractured, that’s a straight fail.
Corrosion is the one process on a car that never runs backwards. A pad can be replaced, a bush can be pressed out, fluid can be flushed — but lost steel section does not come back, and nothing applied to the surface undoes the pitting underneath. That is why this advisory only ever moves in one direction.
The advisory decoder covers the other phrases you might have alongside this one — springs rarely corrode alone on a car of that age.
How long have you got?
There’s no fixed timetable, and anyone who gives you one is guessing. What we can tell you is the pattern: corroded springs don’t degrade gracefully and then warn you. They hold, and hold, and then fail suddenly — most often in winter, when cold makes tired steel more brittle and the first hard pothole finishes the job.
That’s why the honest answer to “can it wait?” is: it can wait until it can’t, and you won’t get notice. If you’ve been given this advisory in spring or summer, you have a genuine window — use it. If you’ve been given it in November, treat it as more urgent than the word “advisory” suggests.
The corner matters less than you’d think. Springs corrode at similar rates on both sides of an axle because they share the same conditions, so one flagged spring usually means its partner isn’t far behind — which is part of why they’re replaced in pairs.
When “corroded” becomes “fractured”
A fractured coil spring is an automatic MOT failure, and rightly so — a broken spring compromises both handling and braking, and a loose coil end can catch the tyre next to it.
You’ll usually know when it happens. Sometimes there’s an audible crack over a bump; more often the first sign is a corner sitting visibly lower than the others, or a metallic clonk and grinding on full steering lock as the broken end catches. Any of those means stop treating it as a noise and book it.
The advisory is the cheap moment. The same pair of springs costs the same whether you fit them in July or after a breakdown in December — but in July you choose the garage, the timing and the quote, and you don’t pay for recovery or a ruined tyre alongside.
How often does this advisory become a failure?
We can put a number on it. The DVSA test record tracks every advisory from one MOT to the next, so it’s possible to measure what actually happened to 27 million suspension advisories rather than guess.
| What happened next | Suspension | Brake parts | Tyres |
|---|---|---|---|
| Became a failure at a later test | 18.7% | 9.4% | 9.9% |
| Ignored, no action taken | 37.1% | 36.1% | 30.5% |
| Fixed | 44.2% | 54.4% | 59.6% |
| Median advisory to failure | 376 days — the next MOT | ||
Calculated from the DVSA MOT test database (Open Government Licence v3.0), from 27,042,129 tracked suspension advisories. The record groups springs with the rest of the suspension — arms, bushes, dampers and links — so these figures describe the category this advisory belongs to, not springs alone.
Suspension has the highest conversion rate of any advisory category — nearly one in five comes back as a failure, roughly twice the rate of brakes or tyres. It also has the lowest fix rate of anything measured: fewer than half get dealt with.
Those two facts belong together. Worn brake pads squeal. A worn tyre is visible in the drive. A corroded spring does neither — it makes no sound, lights no warning lamp, and the car drives exactly as it did before. So it gets postponed, and the median gap between the advisory and the failure is 376 days: precisely one MOT cycle. Drivers aren’t reacting to the spring. They’re reacting to the next test.
A conversion rate measures what was found at the following MOT, which works for wear that creeps steadily towards a threshold. A corroded spring does not creep. It holds until one cold morning when it doesn’t — and a car with a snapped spring is usually recovered rather than driven to a test.
Those cases never reach the column above. The spring failed, the owner paid, and the national record has no line for it because no tester ever saw the car. So read 18.7% as a floor: suspension advisories are already the ones most likely to come back, and within that category this is the one that does not wait politely for a test date.
The same figure runs the other way on a misting damper, where it overstates the risk because the inspection manual specifically excludes slight seepage from rejection. One defect code, two opposite readings, depending on which part the tester wrote down.
What it costs to put right
| Job | Price fitted | Notes |
|---|---|---|
| Coil springs, axle pair | £130–£320 | The standard job — always done in pairs |
| Single spring | Rarely right | Leaves the car sitting and handling unevenly |
| Damper added while the strut is apart | Ask at the time | Far cheaper now than as a separate visit |
| Alignment afterwards | £40–£80 | New springs change ride height and geometry |
Independent garage prices, parts and labour. Main dealers typically charge around 50% more. Full prices by model on the coil spring replacement cost page, and the wider suspension repair guide covers everything else that lives at the same corner.
A new spring opposite a decade-old one leaves the car sitting unevenly and handling asymmetrically, so a garage quoting for a single spring on an older car isn’t doing you a favour. Springs on the same axle also corrode at similar rates, so the partner is rarely far behind.
The strut has to come apart to change a spring, which is where the labour goes. If your shock absorbers are also flagged, doing both together saves paying for that strip-down twice — the marginal cost of a damper while the strut is already out is far lower than a separate visit.
New springs sit slightly taller than the tired ones they replace, which moves the geometry at that corner. An alignment afterwards is not automatic on every car, but it is worth asking about — particularly if a tyre at that corner has been wearing unevenly.
| Worked example — front pair, family hatchback | |
|---|---|
| Coil springs, pair, quality aftermarket | £45 |
| Labour — 1.5 h × £65 | £98 |
| Typical total, both sides | ≈ £143 |
Sits at the lower end of the £130–£320 range, which runs up to larger and premium cars. Rear springs on many cars are simpler to reach and come in lower again.
Enter your reg — we’ll pull every advisory from every test, show which ones keep repeating, and price them for your exact car.
What to do next
- Book it in the warmer months. If you’ve just had this advisory in spring or summer, that’s your window — a planned £130–£320 job beats a December roadside failure by a wide margin.
- Ask about the other corner. Springs on the same axle age together, so if one is corroded enough to flag, get the other inspected in the same visit rather than paying twice.
- Check whether anything else is due at that corner. If the strut is coming apart anyway, a flagged misting damper or a worn drop link is much cheaper done now than as a separate job later.
- If a pothole is involved when it does break, document it. A photographed hole and an itemised invoice make a council claim possible — for many drivers that’s the difference between paying the full bill and paying part of it.
Coil spring advisory FAQ
Is a corroded coil spring dangerous?
Not at the advisory stage — the spring is still intact and doing its job, which is why the car passed. It becomes dangerous when it fractures, because a broken spring affects handling and braking and a loose coil end can catch a tyre. The advisory is your warning before that point, not the point itself.
How long can I drive with a corroded coil spring?
There’s no reliable timetable — corroded springs hold until they suddenly don’t, most often in winter when cold steel meets a pothole. Treat an advisory received in spring as a genuine planning window, and one received in late autumn as more urgent than the word suggests.
Do coil springs have to be replaced in pairs?
Best practice, yes. A new spring opposite a decade-old one leaves the car sitting unevenly and handling asymmetrically. Springs on the same axle also corrode at similar rates, so if one is bad enough to flag, its partner is rarely far behind — the marginal cost of doing both is small.
Why do coil springs corrode?
Because they sit low in the wheel arch where road salt, spray and grit collect and stay damp. Over years the salt pits the protective coating and then the steel underneath, reducing the section that carries the load. UK winters and gritted roads make it one of the most common suspension advisories on older cars.
Will a corroded spring fail my next MOT?
Only if it fractures, or if the corrosion has progressed enough for the tester to judge the spring no longer serviceable. Corrosion doesn’t reverse, so an advisory this year is a strong candidate for a failure next year — suspension advisories become failures more often than any other category.
Can a corroded coil spring be repaired instead of replaced?
No. There’s no repair for a corroded spring — you can’t restore lost steel section, and treating the surface doesn’t undo the pitting underneath. Replacement in pairs is the only fix, at £130–£320 fitted.
What happens if a coil spring snaps while driving?
The corner drops, handling and braking are affected, and a broken coil end can dig into the tyre beside it. Keep any journey short and gentle and get it booked immediately. It’s an automatic MOT failure regardless, so the pair of springs is coming either way.
Does a corroded spring affect my car’s ride?
Usually not noticeably, which is exactly the problem. The spring keeps carrying the load right up until it fractures, so there’s no gradual softening or noise to warn you. That’s why the MOT advisory is the only real early warning most drivers get.
How often does a coil spring advisory become an MOT failure?
18.7% of suspension advisories return as failures — the highest of any category, against 9.4% for brake parts and 9.9% for tyres. Suspension also has the lowest fix rate: fewer than half get dealt with. And for corroded springs specifically that figure understates the risk, because a snapped spring is usually recovered rather than driven to a test.