MOT failure rate and common problems for the Mercedes 409, and how to check your own car by registration.
Updated 05 September 2026.
Mercedes 409 MOT failure rate
What a Mercedes 409 fails its MOT on, and the part that fixes each.
What it fails on, and why
Lighting is the single most common MOT failure and the cheapest to put right. A blown headlight, brake-light or number-plate bulb, a cracked lens, or a headlamp beam that points too high or low will all fail. Most are a two-minute bulb swap.
Brake failures cover worn pads and discs, an imbalance between wheels, corroded or scored discs, or a binding caliper. Braking efficiency is measured on a rolling road, so a spongy or pulling brake shows up as a low reading.
Exhaust failures cover leaks, insecure mountings and emissions over the limit. A blowing exhaust, a failed lambda reading or a diesel that smokes beyond the limit will fail.
Visibility failures include torn or smearing wiper blades, a washer jet that does not reach the screen, and chips or cracks in the driver's swept area. Blades and washer fluid are quick, cheap fixes.
Tyres fail for tread below the 1.6mm legal limit across the central three-quarters, uneven or exposed-cord wear, or sidewall damage. The tester inspects all four; a single illegal tyre is a fail.
This covers a range of smaller items, from a non-working horn to a warning light left on.
The parts that fix each
If your car has just failed, you have 10 working days to fix the items and get a free partial retest. Confirm the exact fitment against your registration or VIN before buying.
Other models
Questions and answers
What is the MOT failure rate of the Mercedes 409?
It fails 32.8% of its MOT tests across the DVSA record, from 58 tests.
What do these cars fail their MOT on most?
The most common failure area is lamps & electrical, at 57.9% of this model's failures.