Part of the Mercedes-Benz C-Class W205 (2014–2021) guide: best and worst years compared.
2021 Mercedes-Benz C-Class: common problems and what to check
What gets flagged at MOT on 2021 Mercedes-Benz C-Classs, from 5,709 tests in 2025, plus known faults and what to look at before you buy one.
What stands out
Parts flagged at MOT more often on 2021 Mercedes-Benz C-Classs than on all cars registered in 2021.
- Ball joint3.8× usualMercedes-Benz C-Class2.3% All 2021 cars0.6%
Failed outright at MOT: 0.3%, against 0.2% of all 2021 cars. The rest were advisories or minor defects.
Rough price £60–£150 (one joint) ClickMechanicAt the viewing: Listen for knocking over bumps and check the rubber boots behind the wheels aren't split.
By area
The share of 2021 Mercedes-Benz C-Class MOT tests where testers flagged each area, as a fail or an advisory. Rough prices are typical independent-garage costs.
- Tyres27% 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.
- Brakes8% 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.
- Suspension3% 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.
- Seats and seatbelts1% of testsRough price £80–£250
At the viewing: Pull each seatbelt sharply. It should lock, and retract cleanly.
Known faults
Reported by owners, mechanics and buying guides for this model and age. Check which engine the car has, as some apply to one engine only.
- Diesel emissions system faultsDiesel
Particulate filter, NOx sensor and AdBlue problems are the main worry on diesels, especially ones used for short trips.
At the viewing: Watch for emissions or AdBlue warnings on the dash, and ask what journeys it’s done.
- Air suspensionCars with air suspension
Cars with air suspension can develop expensive faults that need a specialist.
At the viewing: Check the car sits level all round, look for uneven front tyre wear, and watch for suspension warnings.
- Petrol smell or leaks (petrol)Petrol
Petrol models can leak fuel from the pump area or crack plastic air pipes.
At the viewing: Smell around the car after a cold start, and listen for rough idle.
- Automatic gearbox behaviourAutomatic
Some automatics shift inconsistently.
At the viewing: Drive through every gear at different speeds. Any odd or jerky changes should be priced in or a reason to walk away.
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Other years
| Year | MOT tests | Most flagged |
|---|---|---|
| 2022 | 4,604 | Tyres 27% |
| 2020 | 9,919 | Tyres 30% |
| 2019 | 24,634 | Tyres 29% |
| 2018 | 28,346 | Tyres 29% |
| 2017 | 39,535 | Tyres 29% |
| 2016 | 36,616 | Tyres 30% |
| 2015 | 34,042 | Tyres 30% |
| 2014 | 25,210 | Tyres 32% |
| 2013 | 23,494 | Suspension 33% |
| 2012 | 25,753 | Brakes 40% |
| 2011 | 18,838 | Brakes 40% |
| 2010 | 12,845 | Brakes 40% |
| 2009 | 12,668 | Suspension 43% |
| 2008 | 13,214 | Suspension 44% |
| 2007 | 11,454 | Suspension 50% |
| 2006 | 8,786 | Suspension 57% |
| 2005 | 7,282 | Suspension 59% |
| 2004 | 5,380 | Suspension 59% |
| 2003 | 3,648 | Suspension 54% |
| 2002 | 2,021 | Suspension 49% |
| 2001 | 1,080 | Suspension 46% |
| 2000 | 523 | Suspension 41% |
Where this comes from: the DVSA's anonymised results for every MOT test in Great Britain in 2025, counting tests of 2021 Mercedes-Benz C-Classs registered in 2021. "Flagged" includes advisories, so it isn't the same as a fail rate. How we score