2020 Mercedes-Benz B-Class — MOT failures & pass rate
Across 9,578 MOT tests, the 2020 Mercedes-Benz B-Class recorded a 93.2% pass rate. Against MPVs of a similar age (10.9% fail rate), the 2020 B-Class comes out 4.1pp better. Failures cluster in tyres, lighting & signalling and visibility.
What the MOT record shows
No single area dominates — tyres (4.3%) and lighting & signalling (1.5%) 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 brake pads — headlamp aim alone was recorded 139 times.
A 90-120k example is materially riskier than a 0-30k one: 12.1% versus 5.5%.
Fuel type barely separates them — petrol fails 6.4% of the time against 7.2% for diesel.
Advisories point at the next bill rather than this one: tyres was flagged on 19.7% of tests without failing them.
The trend is worsening — 1.8% of tests failed in 2022 against 7.7% in 2025, the usual pattern as a fleet ages.
How it compares
Top failure categories
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Tyres | 4.3% | 411 |
| 2 | Lighting & signalling | 1.5% | 143 |
| 3 | Visibility | 1.5% | 140 |
| 4 | Brakes | 1.0% | 94 |
| 5 | Suspension | 0.5% | 46 |
| 6 | Seat belts & restraints | 0.5% | 46 |
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 | 139 |
| 2 | Wipers | 120 |
| 3 | Brake pads | 87 |
| 4 | Tread depth | 76 |
| 5 | Washers | 40 |
| 6 | SRS malfunction indicator lamp | 24 |
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 | 19.7% | 1,891 |
| 2 | Brakes | 6.4% | 610 |
| 3 | Other defects | 3.9% | 371 |
| 4 | Visibility | 3.1% | 294 |
| 5 | Suspension | 1.7% | 159 |
| 6 | Road wheels | 0.4% | 41 |
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 | 6,665 | 5.5% |
| 30-60k | 2,620 | 9.3% |
| 60-90k | 252 | 11.9% |
| 90-120k | 33 | 12.1% |
Failure rate by age
By fuel type
| Fuel | Tests | Fail rate |
|---|---|---|
| Petrol | 5,761 | 6.4% |
| Diesel | 3,558 | 7.2% |
| Hybrid | 259 | 7.3% |
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2022 | 108 | 1.8% |
| 2023 | 3,213 | 6.2% |
| 2024 | 3,118 | 6.5% |
| 2025 | 3,127 | 7.7% |
What to check before buying a 2020 B-Class
On a 2020 B-Class, tyres is what the MOT record says goes wrong most — it appeared in 4.3% of tests. Check these areas before you commit.
- Tyres (4.3% 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 (1.5% of tests): Often a cheap bulb, but persistent issues can mean wiring or corrosion in the units. Typical repair: £10–£150.
- Visibility (1.5% 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 2020 Mercedes-Benz B-Classs pass their MOT?
93.2% of the 9,578 2020 Mercedes-Benz B-Class MOT tests in this dataset passed — a 6.8% fail rate.
What is the most common MOT failure on a 2020 Mercedes-Benz B-Class?
Tyres, recorded in 4.3% of tests, followed by lighting & signalling (1.5%).
Does the 2020 B-Class get worse with mileage?
Its MOT fail rate rises from 5.5% in the 0-30k band to 12.1% in the 90-120k band.
Methodology & source. Based on 9,578 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.