2021 Mercedes-Benz B-Class: common problems and MOT failures
What MOT testers find on the Mercedes-Benz B-Class first registered in 2021: we looked at the 1,807 MOTs these cars had during 2025. Plus known faults and what to look at before you buy one.
Common 2021 Mercedes-Benz B-Class MOT failures and advisories
The share of 2021 Mercedes-Benz B-Class MOT tests where testers flagged each area, as a fail or an advisory. Rough prices are typical independent-garage costs.
- Tyres21% of testsRough price £70–£150
At the viewing: Check the tread on all four tyres, including the inside edges, and look for cracks or bulges.
- Brakes6% of testsRough price £150–£350
At the viewing: Look for a lip on the disc edges and feel for judder or pulling when braking firmly from about 40mph.
- Wipers, windscreen and mirrors5% of testsRough price £15–£250
At the viewing: Check for chips in the driver's view, and test the wipers and washers.
- Lights and electrics4% of testsRough price £10–£80
At the viewing: Ask a friend to check every light, including brake lights and indicators, while you operate them.
- Seats and seatbelts2% of testsRough price £80–£250
At the viewing: Pull each seatbelt sharply. It should lock, and retract cleanly.
- Suspension2% of testsRough price £120–£400
At the viewing: Listen for knocks over speed bumps, and look behind each front wheel for a snapped coil spring.
Questions to ask the seller before buying a 2021 Mercedes-Benz B-Class
Ask before you travel to see it. A seller who knows the car will have answers, and receipts.
- Can I see the service history and receipts for any big jobs?
Looking at a Mercedes-Benz B-Class?
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Other years
Every year of the Mercedes-Benz B-Class compared
| Year | MOT tests | Most flagged |
|---|---|---|
| 2026 | – | Too new for MOT data |
| 2025 | – | Too new for MOT data |
| 2024 | – | Too new for MOT data |
| 2023 | – | Too new for MOT data |
| 2022 | 1,310 | Tyres 20% |
| 2020 | 2,909 | Tyres 24% |
| 2019 | 599 | Tyres 25% |
| 2018 | 3,892 | Tyres 31% |
| 2017 | 5,689 | Tyres 29% |
| 2016 | 5,353 | Tyres 31% |
| 2015 | 5,654 | Tyres 32% |
| 2014 | 8,185 | Tyres 32% |
| 2013 | 6,957 | Tyres 33% |
| 2012 | 5,658 | Tyres 32% |
| 2011 | 3,373 | Brakes 42% |
| 2010 | 4,279 | Brakes 44% |
| 2009 | 3,989 | Brakes 48% |
| 2008 | 3,072 | Brakes 51% |
| 2007 | 2,249 | Brakes 47% |
| 2006 | 1,611 | Brakes 51% |
| 2005 | 324 | Brakes 48% |
Where this comes from: the DVSA's anonymised results for every MOT test done in Great Britain during 2025, counting the MOTs of Mercedes-Benz B-Class cars first registered in 2021. "Flagged" includes advisories, so it isn't the same as a fail rate. How we score