2018 Mercedes-Benz B-Class — MOT failures & pass rate
21,901 MOT tests on the 2018 Mercedes-Benz B-Class are in this dataset, and 90.2% of them passed. That is 2.4 percentage points better than MPVs of a similar age, which fail at 12.2%. Failures cluster in tyres, lighting & signalling and visibility.
What the MOT record shows
No single area dominates — tyres (5.9%) and lighting & signalling (3.1%) are close, so failures are spread across several systems rather than one weak point.
At component level the recurring items are registration plate lamp(s), headlamp aim and brake pads — registration plate lamp(s) alone was recorded 449 times.
A 150k+ example is materially riskier than a 0-30k one: 19.4% versus 7.5%.
The petrol cars hold up better: 8.7% fail against 11.0% for diesel, a 2.3-point gap across 21,895 tests.
Tyres is the most common advisory, noted on 22.0% of tests — work that passed today but is likely due soon.
The trend is worsening — 7.9% of tests failed in 2021 against 12.4% in 2025, the usual pattern as a fleet ages.
How it compares
Top failure categories
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Tyres | 5.9% | 1,303 |
| 2 | Lighting & signalling | 3.1% | 680 |
| 3 | Visibility | 1.5% | 321 |
| 4 | Brakes | 1.2% | 264 |
| 5 | Suspension | 0.8% | 171 |
| 6 | Emissions & environmental | 0.5% | 104 |
Most common specific failures
The exact components most often recorded as failures — more specific than the categories above.
| # | Failure item | Times recorded |
|---|---|---|
| 1 | Registration plate lamp(s) | 449 |
| 2 | Headlamp aim | 308 |
| 3 | Brake pads | 241 |
| 4 | Wipers | 223 |
| 5 | Tread depth | 219 |
| 6 | Washers | 140 |
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 | 22.0% | 4,809 |
| 2 | Brakes | 10.2% | 2,237 |
| 3 | Other defects | 6.4% | 1,394 |
| 4 | Visibility | 2.8% | 604 |
| 5 | Lighting & signalling | 2.1% | 465 |
| 6 | Road wheels | 1.1% | 234 |
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 | 12,105 | 7.5% |
| 30-60k | 7,953 | 11.8% |
| 60-90k | 1,500 | 15.8% |
| 90-120k | 241 | 21.2% |
| 120-150k | 64 | 18.8% |
| 150k+ | 36 | 19.4% |
Failure rate by age
By fuel type
| Fuel | Tests | Fail rate |
|---|---|---|
| Diesel | 11,179 | 11.0% |
| Petrol | 10,716 | 8.7% |
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2021 | 4,323 | 7.9% |
| 2022 | 4,379 | 8.4% |
| 2023 | 4,401 | 9.7% |
| 2024 | 4,348 | 10.8% |
| 2025 | 4,450 | 12.4% |
What to check before buying a 2018 B-Class
The failure pattern for this year is specific enough to inspect against: tyres accounted for 5.9% of tests. Start there.
- Tyres (5.9% 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 (3.1% 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 2018 Mercedes-Benz B-Classs pass their MOT?
90.2% of the 21,901 2018 Mercedes-Benz B-Class MOT tests in this dataset passed — a 9.8% fail rate.
What is the most common MOT failure on a 2018 Mercedes-Benz B-Class?
Tyres, recorded in 5.9% of tests, followed by lighting & signalling (3.1%).
Does the 2018 B-Class get worse with mileage?
Its MOT fail rate rises from 7.5% in the 0-30k band to 19.4% in the 150k+ band.
Methodology & source. Based on 21,901 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.