Mercedes-Benz C300d — MOT pass rate & failures
7,964 MOT tests on the Mercedes-Benz C300d (2014–2023) give an 88.4% pass rate. That is 6.3 percentage points better than the 17.9% fail rate across all Mercedes-Benz C-Class versions, so the C300d is a stronger pick within the range. Failures concentrate in tyres, lighting & signalling and visibility.
What the MOT record shows
At component level the recurring items are tread depth, headlamp aim and ball joint — tread depth alone was recorded 286 times.
Mileage matters less than usual here: the C300d fails 8.5% of the time in the 0-30k band and 9.7% at 120-150k, a spread of only 1.2 points.
Tyres is the most common advisory, noted on 25.1% of tests — work that passed today but is likely due soon.
The trend is worsening — 6.6% of tests failed in 2022 against 12.3% in 2025, the usual pattern as a fleet ages.
How it compares
By model year
| Year | Tests | Pass rate | Fail rate |
|---|---|---|---|
| 2019 | 1,175 | 89.5% | 10.5% |
| 2020 | 4,299 | 88.0% | 12.0% |
| 2021 | 2,031 | 88.1% | 11.9% |
| 2022 | 370 | 89.7% | 10.3% |
| 2023 | 62 | 93.5% | 6.5% |
Top failure categories
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Tyres | 8.4% | 670 |
| 2 | Lighting & signalling | 1.4% | 111 |
| 3 | Visibility | 1.3% | 106 |
| 4 | Suspension | 1.3% | 102 |
| 5 | Road wheels | 1.0% | 83 |
| 6 | Brakes | 0.8% | 63 |
| 7 | Emissions & environmental | 0.5% | 44 |
| 8 | Other defects | 0.4% | 30 |
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 | 286 |
| 2 | Headlamp aim | 139 |
| 3 | Ball joint | 72 |
| 4 | Wipers | 70 |
| 5 | Brake pads | 53 |
| 6 | Malfunction indicator lamp | 44 |
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 | 25.1% | 1,998 |
| 2 | Brakes | 8.3% | 658 |
| 3 | Other defects | 4.4% | 347 |
| 4 | Visibility | 4.1% | 330 |
| 5 | Suspension | 3.4% | 268 |
| 6 | Body, structure & corrosion | 2.2% | 176 |
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 | 2,392 | 8.5% |
| 30-60k | 3,745 | 13.1% |
| 60-90k | 1,382 | 12.6% |
| 90-120k | 346 | 13.6% |
| 120-150k | 72 | 9.7% |
Failure rate by age
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2022 | 347 | 6.6% |
| 2023 | 1,816 | 10.9% |
| 2024 | 2,752 | 11.9% |
| 2025 | 3,041 | 12.3% |
What to check before buying a Mercedes-Benz C300d
Focus on the areas it most often fails on — and remember MOT data covers testable defects only, not engine or gearbox health.
- Tyres (8.4% 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 (1.4% 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 reliable is the Mercedes-Benz C300d at MOT time?
88.4% of the 7,964 Mercedes-Benz C300d MOT tests in this dataset passed — a 11.6% fail rate, better than the 17.9% average across all C-Class versions.
What is the most common MOT failure on a Mercedes-Benz C300d?
Tyres, recorded in 8.4% of tests, followed by lighting & signalling (1.4%).
Does the C300d get worse with mileage?
Its MOT fail rate rises from 8.5% in the 0-30k band to 9.7% in the 120-150k band.
Methodology & source. Based on 7,964 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.