2021 Mercedes-Benz B-Class — MOT failures & pass rate
3,947 MOT tests on the 2021 Mercedes-Benz B-Class are in this dataset, and 93.5% of them passed. MPVs of a similar age fail 10.4% of the time, so this is 3.9pp better than the group it competes with. Failures cluster in tyres, lighting & signalling and visibility.
What the MOT record shows
No single area dominates — tyres (4.5%) and lighting & signalling (1.6%) are close, so failures are spread across several systems rather than one weak point.
At component level the recurring items are headlamp aim, wipers and tread depth — headlamp aim alone was recorded 58 times.
Mileage is the strongest signal on the record: 5.5% of 0-30k cars fail, rising to 9.7% once past 60-90k.
The diesel cars hold up better: 5.6% fail against 7.9% for hybrid, a 2.3-point gap across 1,865 tests.
Tyres is the most common advisory, noted on 16.3% of tests — work that passed today but is likely due soon.
How it compares
Top failure categories
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Tyres | 4.5% | 178 |
| 2 | Lighting & signalling | 1.6% | 61 |
| 3 | Visibility | 1.4% | 55 |
| 4 | Brakes | 0.5% | 21 |
| 5 | Seat belts & restraints | 0.3% | 13 |
| 6 | Suspension | 0.3% | 11 |
Most common specific failures
The exact components most often recorded as failures — more specific than the categories above.
| # | Failure item | Times recorded |
|---|---|---|
| 1 | Headlamp aim | 58 |
| 2 | Wipers | 49 |
| 3 | Tread depth | 18 |
| 4 | Brake pads | 15 |
| 5 | Washers | 14 |
| 6 | Registration plates | 11 |
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 | 16.3% | 643 |
| 2 | Other defects | 4.5% | 176 |
| 3 | Brakes | 4.3% | 171 |
| 4 | Visibility | 3.2% | 127 |
| 5 | Suspension | 1.5% | 60 |
| 6 | Lighting & signalling | 0.6% | 24 |
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 | 2,800 | 5.5% |
| 30-60k | 1,016 | 9.1% |
| 60-90k | 103 | 9.7% |
Failure rate by age
By fuel type
| Fuel | Tests | Fail rate |
|---|---|---|
| Petrol | 2,082 | 6.6% |
| Diesel | 1,160 | 5.6% |
| Hybrid | 705 | 7.9% |
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2023 | 74 | 5.4% |
| 2024 | 1,930 | 6.5% |
| 2025 | 1,920 | 6.5% |
What to check before buying a 2021 B-Class
The failure pattern for this year is specific enough to inspect against: tyres accounted for 4.5% of tests. Start there.
- Tyres (4.5% 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 (1.4% 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 B-Classs pass their MOT?
93.5% of the 3,947 2021 Mercedes-Benz B-Class MOT tests in this dataset passed — a 6.5% fail rate.
What is the most common MOT failure on a 2021 Mercedes-Benz B-Class?
Tyres, recorded in 4.5% of tests, followed by lighting & signalling (1.6%).
Does the 2021 B-Class get worse with mileage?
Its MOT fail rate rises from 5.5% in the 0-30k band to 9.7% in the 60-90k band.
Methodology & source. Based on 3,947 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.