Why cars fail their MOT on corrosion and body structure
Body, chassis and structure faults fail 3.18 percent of car MOTs, and can turn a cheap car into scrap. What fails and why it matters most on salvage.
MOT DATA · 4 min read
Less common but more serious
Body, chassis and structure faults appear on 3.18 percent of car MOTs. That is lower down the list than lights or suspension, but it is the category that matters most, because corrosion to a load-bearing area is the fault most likely to write a car off rather than just cost a few parts.
What fails
The MOT looks for corrosion within a prescribed distance of mounting points and load-bearing structure: sills, chassis rails, suspension and subframe mounts, and seat belt anchorages. Surface rust is fine; structural rot that weakens a mounting is a fail, and welding is often the only fix.
What it costs
This is where costs get unpredictable. A small welding repair on a sill might be a hundred or two at a good welder. Serious rot across chassis rails or subframe mounts can cost more than the car is worth, which is exactly why heavily corroded older cars get scrapped rather than repaired.
The salvage angle
For a flipper this is the one category to take seriously. A structural corrosion fail is not a cheap-consumable buy, it is the risk of a car that can never be economically saved. On accident salvage, structural damage from the impact sits in the same bracket. When the title or the damage points at structural work, the Analyzer treats frame and structural repair as a major cost, and so should you.