MOT advisory explained
“Vehicle structure is corroded”
Rust on the body shell itself, most often the sills or a chassis rail, that has not yet weakened the car. It is the advisory that decides whether an old car has a future, and the models it hits hardest are the ones people expect to last forever.
The tester found rust on a load-bearing part of the body, probed it, and judged that the metal is still doing its job. This is not a bolt-on part. The sills, chassis legs and cross members are the car.
4.9% fail on the body structure at the next test and 25.5% are advised again unchanged. The figure is modest because body steel is thick and rusts slowly, but unlike every other corrosion advisory, this one has no replacement part. The repair is welding.
Rust within thirty centimetres of a suspension or seat belt mounting is a separate, stricter test with its own wording. If yours mentions a mounting, read the page for corrosion near a mounting instead. That one fails twice as often.
A “vehicle structure is corroded but structural rigidity is not significantly reduced” advisory means rust has been found on a load-bearing part of the body, usually a sill or chassis rail, but the tester judged it still strong, so the car passes. Body rust cannot be replaced, only welded. According to DVSA MOT data analysed by PriceMyRepair, 4.9% of 1.2 million such advisories followed to the next test failed on the vehicle structure, and 25.5% were advised again.
What counts as structure
The sills. “sill” is the most common note by a wide margin, with “inner sill” and “outer sill” next. The sill is the box section running under each door. It ties the front of the car to the back, it is where the jack goes, and it is the lowest sealed cavity on the car, so water collects inside it. Rust usually starts on the inside and shows late.
The chassis. “chassis”, “chassis leg” and “chassis rail” between them are the second group. On a car with a separate chassis, the pickups and 4x4s below, the rails are exposed to everything the road throws up and are rarely painted after they leave the factory.
The difference between corroded and weakened. The tester presses with a tool and listens. Surface rust and light scale on a sound section is this advisory. Metal that flexes, flakes in layers or gives way under the probe is a failure, and the words change from “not significantly reduced” to “significantly reduced”.
Will it fail next year?
Two wordings share this page. Together they have been recorded 3,885,732 times, with 1,233,347 followed to the same vehicle’s next MOT.
| What happened at the next test | Share |
|---|---|
| Failed on the same component | 4.9% |
| Failed on anything under defect 6.1.1 | 6.8% |
| Same advisory recorded again | 25.5% |
According to DVSA MOT data analysed by PriceMyRepair: 1,233,347 advisories followed to the same vehicle’s next test. Rows can overlap.
Among the corrosion advisories it sits in the middle. A subframe, which unbolts, fails only 2.0% of the time. Rust near a mounting, judged to a stricter standard, fails 10.2%. Brake pipes fail 10.1%.
A quarter are carried over unchanged. On an older car this line often stays on the certificate for years and the car passes each time. The question is not whether it will fail next year. It is whether the car is worth welding when it does.
| Advisory wording | Fails on same part | Advised again | Followed |
|---|---|---|---|
| Suspension component mounting prescribed area is corroded | 10.2% | 24.2% | 1,521,106 |
| Brake pipe corroded, covered in grease or other material | 10.1% | 44.4% | 7,889,073 |
| Coil spring corroded | 5.0% | 39.1% | 4,780,118 |
| Vehicle structure is corroded but structural rigidity is not significantly reduced | 4.9% | 25.5% | 1,233,347 |
| Integral body structure or chassis corroded within 30cm of a mounting, | 4.7% | 15.2% | 289,591 |
| Sub-frame corroded | 2.0% | 39.8% | 2,445,675 |
| Macpherson strut corroded | 1.6% | 22.5% | 370,013 |
Cars under seven years old hardly ever get this advisory. From then on it climbs steeply, from 1.1 per 1,000 tests at 7–9 years to 45.6 at 20 years and over, which is nearly one test in twenty. The share that fail next time rises with it, from 1.6% to 6.3%.
| Age of car | Per 1,000 tests | Fails on same part | Followed |
|---|---|---|---|
| 7–9 years | 1.1 | 1.6% | 41,118 |
| 10–12 years | 5.6 | 3.4% | 178,511 |
| 13–15 years | 15.9 | 4.7% | 348,032 |
| 16–19 years | 30.0 | 5.4% | 398,153 |
| 20 years and over | 45.6 | 6.3% | 234,525 |
Treating body rust early is cheap: clean back to metal, convert, seal, and cavity wax inside the sills. Welding it later is not. A sill repair on a common hatchback can cost more than the car is worth, and the same job on a Defender or a classic is routine.
So the decision is about the car, not the rust. If you plan to keep it, protect it this year. If it is a runabout with two years left in it, this advisory asks nothing of you.
If you are buying a car with this on its history, ask where. A rusty sill on a fifteen-year-old car is normal. A rusty chassis rail on a ten-year-old one is a car that has been somewhere wet.
Exact wording on your certificate
Two wordings, one for the vehicle structure and one for an integral body, describe the same thing. The failure uses the opposite ending.
| Line on the certificate | Result | Code |
|---|---|---|
| Vehicle structure is corroded but structural rigidity is not significantly reduced | Advisory — pass | 6.1.1 (c) (i) |
| Integral body structure is corroded but structural rigidity is not significantly reduced | Advisory — pass | 6.1.1 (c) (i) |
| Vehicle structure is corroded and structural rigidity is significantly reduced | Major — fail | 6.1.1 (c) (ii) |
A third of entries have no position at all, because a sill runs the length of the car and a tester who writes “all” is describing the whole underside. Where a position is given, the rear is well ahead of the front. The rear of a car sits in the spray from its own wheels, and rear wheel arches and the back of the sills are where the mud packs in.
| Position written by the tester | Share of all instances |
|---|---|
| No position recorded | 35% |
| Rear | 14% |
| Offside rear | 10% |
| Nearside rear | 9% |
| Offside front | 6% |
| Nearside front | 5% |
From 3,885,732 recorded instances. Testers can add their own note after the standard wording. The most common on this advisory: “sill” (124,394), “chassis” (32,442), “inner sill” (29,056), “outer sill” (23,075), “both sides” (16,201), “chassis leg” (13,950), “wheel arch” (10,737), “cross member” (10,481).
What it costs
There is no standard price for structural rust. Cleaning and cavity waxing is a modest labour job, and worth having done at the next service if you are keeping the car. Welding repairs are quoted per section and vary from a small patch to replacing a whole sill, so any range we gave would be misleading. Ask for a quote for the specific area named. Other prices are on the repair costs index.
Can I still drive with this advisory?
There is nothing to feel from the driver’s seat. The one thing to do before winter is have the rust treated and the cavities waxed, because salt does most of the damage between October and March.
Enter your reg to see every year this advisory has appeared on your car and whether the tester’s wording has hardened over time.
Which cars get this advisory most?
The all-vehicle average is 4.8 per 1,000 tests. The models below get it up to ten times as often, and they have one thing in common.
| Model | Per 1,000 tests | Vs all cars | Tests |
|---|---|---|---|
| Mitsubishi Shogun | 48 | 10.0× | 420,039 |
| Mitsubishi L200 | 46 | 9.7× | 935,407 |
| Land Rover Discovery | 43 | 8.9× | 1,610,504 |
| Toyota Hilux | 40 | 8.4× | 734,628 |
| Land Rover Defender | 38 | 7.8× | 1,232,451 |
| Nissan Navara | 31 | 6.4× | 712,261 |
| Ford Ranger | 28 | 5.8× | 1,001,179 |
| Ford Transit | 20 | 4.2× | 9,907,752 |
| Mazda MX-5 | 18 | 3.8× | 962,840 |
| Fiat Ducato | 17 | 3.5× | 962,883 |
Model families are grouped by the first word of the DVSA model name, so “Transit” covers every Transit variant. Only models with at least 60,000 tests are ranked.
Every one of the top seven is a body-on-frame 4×4 or pickup: the Mitsubishi Shogun at 10.0 times the average, the Mitsubishi L200, Land Rover Discovery, Toyota Hilux, Land Rover Defender, Nissan Navara and Ford Ranger. A separate chassis is bare steel underneath, and these vehicles spend their lives on farms, sites and salted roads. The Ford Transit and Fiat Ducato are vans, kept for the same reasons.
The Mazda MX-5 is the odd one out: a sports car that lasts, kept long enough for its sills to rust.
What to do next
- Get the location in writing. Sill, chassis leg, cross member, arch. It decides both the cost and the urgency.
- Look at it yourself. A torch under the sill. Brown and rough is fine. Bubbling paint, holes, or metal you can push a screwdriver into is not.
- Treat it before winter. Clean, rust converter, seal, and cavity wax injected into the sills. It is the only cheap moment.
- Decide what the car is to you. Keeper or runabout. The same rust deserves a very different response on each.
Vehicle structure corroded FAQ
What does vehicle structure is corroded but structural rigidity is not significantly reduced mean?
Rust has been found on a load-bearing part of the body, usually a sill or chassis rail, but the tester judged that the metal is still strong enough. It is an advisory and the car passes.
Will corroded sills fail the MOT next year?
Not usually. According to DVSA MOT data analysed by PriceMyRepair, 4.9% of 1.2 million such advisories failed on the vehicle structure at the next test, and 25.5% were given the same advisory again.
Can structural rust be repaired?
Yes, by welding new metal in. Body structure cannot be unbolted and replaced. Early surface rust can be treated and sealed without welding, which is far cheaper.
How much does it cost to fix?
It depends entirely on where and how much. Treating surface rust is a modest labour job. Welding is quoted per section, from a small patch to a full sill. Any prices we publish are estimates and final quotes come from garages.
Is it safe to drive with structural corrosion?
Yes, while the tester judges it not to have reduced the car’s rigidity, which is the condition for this advisory. There are no symptoms to watch for.
Which vehicles get this advisory most?
Body-on-frame 4x4s and pickups. The Mitsubishi Shogun, Mitsubishi L200 and Land Rover Discovery get it around nine to ten times as often as the average vehicle, because a separate chassis is bare steel exposed to the road.
How these figures were calculated. According to DVSA MOT data analysed by PriceMyRepair, from the DVSA anonymised MOT test results (Open Government Licence v3.0): 350,943,111 tests. This advisory was recorded 3,885,732 times; 1,233,347 of those were followed to the same vehicle’s next test between 180 and 730 days later. “Fails on the same part” means a failure at that next test under the same defect code and naming the same component, on either side of the vehicle. Testers do not always name a component the same way twice, so the figure is a floor. Method and how to cite.