2018 Mercedes-Benz Sl — MOT failures & pass rate
Across 2,205 MOT tests, the 2018 Mercedes-Benz Sl recorded a 93.1% pass rate. Coupes & convertibles of a similar age fail 9.0% of the time, so this is 2.1pp better than the group it competes with. Failures cluster in tyres, lighting & signalling and suspension.
What the MOT record shows
One area stands out: tyres, recorded in 4.8% of tests against 1.3% for the next-worst category.
At component level the recurring items are headlamp aim, registration plates and ball joint — headlamp aim alone was recorded 28 times.
A 60-90k example is materially riskier than a 0-30k one: 16.4% versus 5.5%.
Tyres is the most common advisory, noted on 14.0% of tests — work that passed today but is likely due soon.
How it compares
Top failure categories
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Tyres | 4.8% | 105 |
| 2 | Lighting & signalling | 1.3% | 28 |
| 3 | Suspension | 0.9% | 19 |
| 4 | Other defects | 0.6% | 13 |
| 5 | Visibility | 0.4% | 8 |
| 6 | Road wheels | 0.2% | 5 |
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 | 28 |
| 2 | Registration plates | 22 |
| 3 | Ball joint | 17 |
| 4 | Tread depth | 13 |
| 5 | Ball joint dust cover | 6 |
| 6 | Tyre pressure monitoring system | 5 |
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 | 14.0% | 309 |
| 2 | Brakes | 2.8% | 61 |
| 3 | Other defects | 2.5% | 54 |
| 4 | Visibility | 1.9% | 42 |
| 5 | Suspension | 1.6% | 36 |
| 6 | Road wheels | 1.3% | 29 |
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 | 1,699 | 5.5% |
| 30-60k | 442 | 11.3% |
| 60-90k | 55 | 16.4% |
Failure rate by age
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2021 | 478 | 7.5% |
| 2022 | 435 | 3.7% |
| 2023 | 447 | 7.4% |
| 2024 | 416 | 8.9% |
| 2025 | 429 | 7.2% |
What to check before buying a 2018 Sl
The failure pattern for this year is specific enough to inspect against: tyres accounted for 4.8% of tests. Start there.
- Tyres (4.8% 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 (1.3% of tests): Often a cheap bulb, but persistent issues can mean wiring or corrosion in the units. Typical repair: £10–£150.
- Suspension (0.9% of tests): Worn drop links, bushes, springs or shocks — listen for knocks over bumps and check for uneven tyre wear. Typical repair: £150–£450 per corner.
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 Sls pass their MOT?
93.1% of the 2,205 2018 Mercedes-Benz Sl MOT tests in this dataset passed — a 6.9% fail rate.
What is the most common MOT failure on a 2018 Mercedes-Benz Sl?
Tyres, recorded in 4.8% of tests, followed by lighting & signalling (1.3%).
Does the 2018 Sl get worse with mileage?
Its MOT fail rate rises from 5.5% in the 0-30k band to 16.4% in the 60-90k band.
Methodology & source. Based on 2,205 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.