2021 Mercedes-Benz C-Class — MOT failures & pass rate
The 2021 Mercedes-Benz C-Class passed 90.1% of its 14,133 recorded MOT tests. Executive cars of a similar age fail at 9.8%, so the 2021 C-Class sits squarely on the average. Failures cluster in tyres, lighting & signalling and visibility.
What the MOT record shows
Tyres dominates the failure mix at 7.5% of all tests — 5.9 points clear of lighting & signalling, so it is the first thing to check.
At component level the recurring items are tread depth, headlamp aim and wipers — tread depth alone was recorded 468 times.
Condition tracks the odometer closely. Failures run at 7.6% in the 0-30k band and 14.3% in the 120-150k band, a 6.6-point spread.
Fuel type barely separates them — hybrid fails 9.3% of the time against 10.3% for diesel.
Advisories point at the next bill rather than this one: tyres was flagged on 22.2% of tests without failing them.
The trend is improving — the fail rate fell from 14.3% in 2021 to 9.9% in 2025, as the worst-kept examples leave the fleet.
How it compares
Top failure categories
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Tyres | 7.5% | 1,065 |
| 2 | Lighting & signalling | 1.6% | 230 |
| 3 | Visibility | 1.3% | 178 |
| 4 | Road wheels | 1.0% | 139 |
| 5 | Suspension | 0.6% | 91 |
| 6 | Brakes | 0.6% | 81 |
Most common specific failures
The exact components most often recorded as failures — more specific than the categories above.
| # | Failure item | Times recorded |
|---|---|---|
| 1 | Tread depth | 468 |
| 2 | Headlamp aim | 297 |
| 3 | Wipers | 128 |
| 4 | Brake pads | 87 |
| 5 | Registration plates | 67 |
| 6 | Washers | 65 |
Top advisory categories
Advisories aren't failures, but they flag work likely needed soon — useful when budgeting.
| # | Category | % of tests with advisory | Tests |
|---|---|---|---|
| 1 | Tyres | 22.2% | 3,143 |
| 2 | Brakes | 6.5% | 923 |
| 3 | Other defects | 4.0% | 560 |
| 4 | Visibility | 3.9% | 550 |
| 5 | Suspension | 1.8% | 250 |
| 6 | Body, structure & corrosion | 1.3% | 187 |
Failure rate by mileage
Higher-mileage cars tend to fail more — often the most useful guide to real condition.
| Mileage band | Tests | Fail rate |
|---|---|---|
| 0-30k | 6,905 | 7.6% |
| 30-60k | 5,806 | 11.7% |
| 60-90k | 1,134 | 12.7% |
| 90-120k | 216 | 13.4% |
| 120-150k | 56 | 14.3% |
Failure rate by age
By fuel type
| Fuel | Tests | Fail rate |
|---|---|---|
| Diesel | 7,817 | 10.3% |
| Hybrid | 5,769 | 9.3% |
| Petrol | 547 | 9.9% |
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2021 | 42 | 14.3% |
| 2023 | 434 | 5.8% |
| 2024 | 6,865 | 10.1% |
| 2025 | 6,780 | 9.9% |
What to check before buying a 2021 C-Class
On a 2021 C-Class, tyres is what the MOT record says goes wrong most — it appeared in 7.5% of tests. Check these areas before you commit.
- Tyres (7.5% of tests): Usually a quick, known-cost fix, but check tread, age and uneven wear (which can hint at alignment or suspension issues). Typical repair: £50–£120 per tyre.
- Lighting & signalling (1.6% of tests): Often a cheap bulb, but persistent issues can mean wiring or corrosion in the units. Typical repair: £10–£150.
- Visibility (1.3% of tests): Wipers, washers, mirrors and screen damage — usually inexpensive, but check for chips in the driver's line of sight. Typical repair: £15–£150.
Repair costs are rough UK ballpark ranges to set expectations, not quotes — actual prices vary widely by car, parts and garage.
Frequently asked questions
How many 2021 Mercedes-Benz C-Classs pass their MOT?
90.1% of the 14,133 2021 Mercedes-Benz C-Class MOT tests in this dataset passed — a 9.8% fail rate.
What is the most common MOT failure on a 2021 Mercedes-Benz C-Class?
Tyres, recorded in 7.5% of tests, followed by lighting & signalling (1.6%).
Does the 2021 C-Class get worse with mileage?
Its MOT fail rate rises from 7.6% in the 0-30k band to 14.3% in the 120-150k band.
Methodology & source. Based on 14,133 MOT tests. Dataset: DVSA MOT testing data (2021,2022,2023,2024,2025). Data last updated 2026-07-27. Figures reflect MOT-testable defects only — read the methodology for how these are calculated and what they don't measure.