MOT defect file
Road spring seat or suspension turret corroded
Last updated
Quick answer
The steel the spring or strut pushes against has rusted through or thinned badly. Because it sits inside a prescribed area, the repair has to be cut out and welded rather than patched or filled.
- Typical cost
- £250–£800
- DIY viability
- Garage job
What you might notice
- Flakes or scabs of rust visible in the engine bay around the top of the strut, often under a rubber cover nobody has lifted in years
- A dull thud or a settling noise from one corner, as the strut works against metal that is no longer solid
- Rust-coloured staining or bubbling paint on the inner wing above the wheel
- Very often no symptom at all — the seat is under the spring or inside the turret and only shows itself when a tester taps it or puts a load through it
What causes it
- Salt and road grit collecting in the spring pan or seat, which is a bowl-shaped trap that stays wet for days
- Blocked or painted-over drain holes in the turret, so water sits inside the box section rather than running out
- Stone damage stripping paint from the seat, then the spring's own movement polishing the bare steel
- Earlier cosmetic repairs — filler or underseal over rust that was never cut back to sound metal — hiding corrosion that carried on underneath
Advisory or failure?
This is a prescribed-area item, which is what makes it serious. Any structure within 30cm of a suspension mounting point is a prescribed area, and corrosion there that has weakened the metal — judged by the tester with finger and thumb pressure or a corrosion assessment tool — is a major defect and a failure. Where the weakening is severe enough to affect the vehicle's structural integrity, or the spring or strut could push through the seat, the grading is dangerous. Surface rust that has not weakened anything is recorded as an advisory or a minor defect. The standard of repair is set out and not negotiable: within a prescribed area the repair must be continuously seam welded and at least as strong as the original panel, so filler, glass fibre, a riveted plate or a coat of underseal over the top will not pass, whatever it looks like.
Can you fix it yourself?
Garage job
This is structural welding on thin, often rotten steel, with a spring under load nearby and fuel or brake lines usually within reach of the torch — it belongs with somebody who welds for a living and can certify the repair. What is genuinely worth doing yourself is the prevention and the inspection: lift the rubber caps in the engine bay and look at the top of each turret, poke the spring seat with a screwdriver where you can reach it, keep the drain holes in the turret clear, and wash salt off the underside through winter. If you find soft metal, get it assessed before booking the test rather than after, because a prescribed-area failure cannot be tidied up overnight.
What it costs
The steel itself costs very little — almost all of this is skilled labour, plus the strip-down needed to reach the area. A single localised spring seat or turret repair with the strut out is typically £250 to £450. Both sides, or a repair that spreads into the inner wing or chassis leg, runs £600 to £800 and beyond. What pushes it up is how much has to come off to reach the rot, how far the corrosion has spread once it is cut back to clean metal, and whether the alignment then needs setting up from scratch. Ask for it to be assessed with the strut out before you commit, because the honest scope is not visible until the cutting starts.
What happens if you ignore it
Corrosion here does not stay still, and it is working on the point where a spring or strut transmits the whole weight of that corner into the body. The failure mode is the strut pushing up through the turret, which happens over a pothole with no warning and takes the steering and the wheel position with it. Financially this is one of the defects most likely to end a car's life: what would have been a £300 patch becomes a £900 rebuild once the inner wing and chassis leg are involved, and on an older car that figure can exceed what it is worth.
Common questions
- Is a corroded spring seat or suspension turret an MOT failure?
- Yes, once the corrosion has weakened the metal. Any structure within 30cm of a suspension mounting point is a prescribed area, and weakened metal there is a major defect, rising to dangerous where the vehicle's structural integrity is affected or the spring could push through the seat. Surface rust that has not weakened anything is recorded as an advisory or a minor defect.
- Can a corroded spring seat be repaired with filler or underseal?
- No. Inside a prescribed area the repair must be continuously seam welded and at least as strong as the original panel, so filler, glass fibre, a riveted plate or a coat of underseal over the top will not pass however tidy it looks. The rot has to be cut back to sound steel and new metal welded in.
- What does a prescribed area mean on an MOT failure?
- It is the structure within 30cm of a critical mounting point, such as a suspension mounting or a steering component attachment. Corrosion there is judged on remaining strength using finger and thumb pressure or a corrosion assessment tool, and the standard of repair is set out rather than left to the garage.
- How do I check my strut tops for rust before an MOT?
- Lift the rubber caps in the engine bay and look at the top of each turret, where flakes of rust often sit under a cover nobody has opened in years. Poke the spring seat with a screwdriver where you can reach it, keep the turret drain holes clear, and look for bubbling paint on the inner wing above the wheel.
- How much does a corroded spring seat repair cost?
- A single localised spring seat or turret repair with the strut out is typically £250 to £450. Both sides, or a repair that spreads into the inner wing or chassis leg, runs £600 to £800 and beyond. The steel itself costs very little, so almost all of this is skilled welding time and the strip-down needed to reach the area.
The warning light behind this
This defect is what a tester writes down. What you see from the driver’s seat is a symbol, and it is worth checking which one, because manufacturers reuse the same shape for more than one system.
This is general guidance, not a diagnosis. The severity DVSA records depends on the specific fault found, so the same item can appear as an advisory on one test and a failure on another. Ask a qualified tester or mechanic to inspect the vehicle.
Has this been recorded on your car?
Check the full MOT history for any UK registration.