At a glance
How 5,769 first tests went in 2025.
- Passed first time
- 87 in every 100
- Did not pass first time
- 13 in every 100749 failed first-attempt tests
- The typical car
- 4 yearsabout 34,142 miles
- First tests counted
- 5,769
What failed most often
- Tyre condition (front)26 in every 100 failed tests
- Tyre tread depth (rear)17 in every 100 failed tests
How we count this. Data: UK MOT open data, 2025. Only Class 4 cars on their first MOT of the year are counted. A car that fails and is fixed at the test station still counts as a fail in the first-attempt rate. These are raw results, not adjusted for age, mileage, or peer mix. The MOT does not test engine or gearbox internals.
These are patterns across 2021 Mercedes-Benz C-Class vehicles in 2025, not a prediction that any one car will have them. Faults are grouped by part of the car. A wear pattern follows age and use more than the way the car was built. They come from MOT defect codes, not manufacturer bulletins, recalls or a diagnosis of any one car.
Road wheels
Two faults. The strongest is the wheel condition (rear): 25 times as often as on similar cars.
Figures below are measured across the 749 failed first attempts in 2025 that had a mileage recorded, which allows a like-for-like comparison.
We only list faults with at least 20 failures and a rate of about 2.0 times that of similar cars, which keeps one-off results out of the list.
Wheel condition (rear)
What it means
A wheel with any fracture or welding defect is graded Dangerous. So is a tyre retaining ring likely to come off, or a wheel distorted or worn to the extent that the wheel or tyre is likely to become detached. A wheel that is badly distorted, or has an excessively worn spigot mounting, is graded Major.
Wheel condition (front)
What it means
A wheel with any fracture or welding defect is graded Dangerous. So is a tyre retaining ring likely to come off, or a wheel distorted or worn to the extent that the wheel or tyre is likely to become detached. A wheel that is badly distorted, or has an excessively worn spigot mounting, is graded Major.
Data: UK MOT open data, 2025. Compared with cars of the same age and mileage.
Suspension
One fault: coil spring (front), 7.7 times as often as on similar cars.
Coil spring (front)
What it means
A missing bump stop rubber is not a reason to fail a coil spring. When the vehicle is jacked and lowered, a spring that does not correctly locate as the suspension returns to its normal running position is rejected as insecurely attached. A missing spring is Major, and graded Dangerous where directional control is affected.
Data: UK MOT open data, 2025. Compared with cars of the same age and mileage.
Tyres
One wear pattern: tyre tread depth (rear), 4.9 times as often as on similar cars.
Tyre tread depth (rear)
What it means
Only primary grooves count when tread depth is assessed: those holding the wear indicators, or cut as deep as those when new. Shallower secondary grooves are ignored. Tread depth below the minimum for the vehicle is Dangerous, and so is a pattern not visible over the whole tread, but that second row applies only to vehicles that need the lower minimum.
Also noted as an advisory
Testers also noted it as an advisory, worn but not yet failing, on 154 first tests, 2.1 times as often as on similar cars.
Data: UK MOT open data, 2025. Compared with cars of the same age and mileage. Advisories count notes recorded on failed first tests only.
Advisories
Other things testers noted as worn or close to failing, more often than on similar cars.
An advisory is a note from the tester about something that has not failed yet. It is an early warning, not a fail. Advisories for the faults above are shown with those faults.
Suspension arm ball joint (front)
Data: UK MOT open data, 2025. Counts cover advisories recorded on failed first tests only, compared with cars of the same age and mileage.
MOT pass rates
How first tests ended, and how the pass rates are counted.
- Passed first time
- 87in every 100
- Passed on the first test.
- Fixed at the station
- 2in every 100
- Failed, then fixed at the test station the same day.
- Failed
- 11in every 100
- Did not pass, and were not fixed at the test station.
First-attempt pass 87.0% of 5,769 first tests (2025): only cars that passed first time count. Official-style pass 88.9%: cars fixed at the test station also count as a pass. The 2 fixed and the 11 not fixed make the 13 in every 100 that did not pass first time.
By fuel type
Figures are in every 100 first tests. Cars with more miles usually fail more often, so the same-mileage figure gives every fuel the mileage mix of all the cars in this year.
Same model, other years
Passed first time in every 100, all tested in 2025.
Newer cars are younger, so look for a jump rather than the climb. A year earlier (2024), when these cars were a year younger, 86 in every 100 passed first time.
| Year | Passed first time | First tests |
|---|---|---|
| 1996 | 72 in every 100 | 347 |
| 1997 | 68 in every 100 | 584 |
| 1998 | 71 in every 100 | 723 |
| 1999 | 68 in every 100 | 644 |
| 2000 | 66 in every 100 | 501 |
| 2001 | 64 in every 100 | 1,041 |
| 2002 | 63 in every 100 | 1,935 |
| 2003 | 58 in every 100 | 3,438 |
| 2004 | 58 in every 100 | 5,099 |
| 2005 | 59 in every 100 | 6,889 |
| 2006 | 58 in every 100 | 8,303 |
| 2007 | 61 in every 100 | 10,849 |
| 2008 | 63 in every 100 | 12,485 |
| 2009 | 64 in every 100 | 11,974 |
| 2010 | 66 in every 100 | 12,159 |
| 2011 | 67 in every 100 | 17,849 |
| 2012 | 67 in every 100 | 24,448 |
| 2013 | 69 in every 100 | 22,380 |
| 2014 | 75 in every 100 | 24,165 |
| 2015 | 78 in every 100 | 32,615 |
| 2016 | 80 in every 100 | 34,859 |
| 2017 | 81 in every 100 | 37,580 |
| 2018 | 84 in every 100 | 26,966 |
| 2019 | 85 in every 100 | 23,530 |
| 2020 | 86 in every 100 | 9,433 |
| 2021 This car | 87 in every 100 | 5,769 |
| 2022 | 89 in every 100 | 4,378 |
If you are buying one
What this year's MOT record means for the decision in front of you.
Mileage matters most on a 2021 C-Class.
Of 2021 C-Class vehicles with under 22,000 miles, 91 in every 100 passed their 2025 MOT first time. With 51,000 miles or more, 83 in every 100 did.
What to check at your mileage
How often each fault turned up on a failed first test, by the car's mileage. Read it as: what is likely to need looking at on a car like the one in front of you.
| Under 22,000 | 30,000–39,000 | 51,000 and over | |
|---|---|---|---|
| Tyre condition (front) | 2.9 | 3.9 | 3.1 |
| Tyre tread depth (rear) | 1.1 | 2.4 | 3.0 |
Faults per 100 first tests, by the car's mileage at the test.
When a car fails
of failed cars had one item to fix.
of failed cars had three or more items to fix.
of all first tests had a defect the tester marked dangerous (unsafe to drive away).
Every figure here is a first-attempt MOT rate from DVSA open data for this model line, for cars of this model year tested in 2025. Each mileage band holds a fifth of the tests. MOTs do not test engine or gearbox internals, so this is a pre-purchase checklist, not a full reliability score.
FAQs
Short answers about how to read this model-year guide.
About this data
How this page is built and what it can (and can't) say.
These figures come from UK MOT open data for this model year. We surface common failure patterns against similar cars, not a full reliability score, and not a pass/fail verdict on any individual vehicle.
What we include
UK Class 4 cars only. Normal MOT tests (not retests); first test per vehicle per calendar year; results pass, PRS, or fail.
Same-day repairs
PRS means the car failed items that were fixed at the test station and then passed the same day. We count PRS as a first-attempt fail in headline rates so same-day repairs do not hide problems.
How we compare
We compare this model year with other Class 4 cars of similar age and mileage in the same test year. This model family is left out of the peer group so the car is not measured against itself.
What this does not cover
- MOTs do not cover engine internals, gearboxes, or many electronics; this is not a full reliability score.
- Common faults come from MOT defect stats, not manufacturer TSBs or recalls.
- Age and mileage matching reduces, but does not remove, differences in how cars were used and maintained.
- If the data for a car is too thin to say anything useful, we say so rather than guess.
Contains public sector information licensed under the Open Government Licence v3.0.
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