2021 Mercedes-Benz S-Class — MOT failures & pass rate
The 2021 Mercedes-Benz S-Class passed 93.4% of its 1,766 recorded MOT tests. Against executive cars of a similar age (9.1% fail rate), the 2021 S-Class comes out 2.6pp better. Failures cluster in tyres, lighting & signalling and brakes.
What the MOT record shows
Tyres dominates the failure mix at 4.7% of all tests — 3.9 points clear of lighting & signalling, so it is the first thing to check.
At component level the recurring items are brake pads, headlamp aim and malfunction indicator lamp — brake pads alone was recorded 14 times.
Mileage matters less than usual here: the 2021 S-Class fails 5.4% of the time in the 0-30k band and 7.3% at 90-120k, a spread of only 1.9 points.
Advisories point at the next bill rather than this one: tyres was flagged on 14.6% of tests without failing them.
The trend is worsening — 6.5% of tests failed in 2021 against 9.0% in 2025, the usual pattern as a fleet ages.
How it compares
Top failure categories
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Tyres | 4.7% | 83 |
| 2 | Lighting & signalling | 0.9% | 15 |
| 3 | Brakes | 0.8% | 14 |
| 4 | Emissions & environmental | 0.6% | 11 |
| 5 | Suspension | 0.6% | 10 |
| 6 | Visibility | 0.4% | 8 |
Most common specific failures
The exact components most often recorded as failures — more specific than the categories above.
| # | Failure item | Times recorded |
|---|---|---|
| 1 | Brake pads | 14 |
| 2 | Headlamp aim | 13 |
| 3 | Malfunction indicator lamp | 10 |
| 4 | Tread depth | 10 |
| 5 | Ball joint | 9 |
| 6 | Registration plates | 6 |
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 | 14.6% | 258 |
| 2 | Brakes | 6.3% | 111 |
| 3 | Visibility | 2.6% | 46 |
| 4 | Suspension | 2.1% | 37 |
| 5 | Other defects | 1.6% | 28 |
| 6 | Road wheels | 0.4% | 8 |
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 | 779 | 5.4% |
| 30-60k | 651 | 8.0% |
| 60-90k | 220 | 4.5% |
| 90-120k | 82 | 7.3% |
Failure rate by age
By fuel type
| Fuel | Tests | Fail rate |
|---|---|---|
| Diesel | 1,137 | 5.7% |
| Hybrid | 476 | 8.0% |
| Petrol | 153 | 8.5% |
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2021 | 31 | 6.5% |
| 2022 | 85 | 3.5% |
| 2023 | 198 | 2.0% |
| 2024 | 711 | 5.6% |
| 2025 | 741 | 9.0% |
What to check before buying a 2021 S-Class
On a 2021 S-Class, tyres is what the MOT record says goes wrong most — it appeared in 4.7% of tests. Check these areas before you commit.
- Tyres (4.7% 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 (0.9% of tests): Often a cheap bulb, but persistent issues can mean wiring or corrosion in the units. Typical repair: £10–£150.
- Brakes (0.8% of tests): Pads/discs are routine wear; binding, imbalance or corroded pipes are more serious — test for pulling under braking. Typical repair: £100–£350 per axle.
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 S-Classs pass their MOT?
93.4% of the 1,766 2021 Mercedes-Benz S-Class MOT tests in this dataset passed — a 6.6% fail rate.
What is the most common MOT failure on a 2021 Mercedes-Benz S-Class?
Tyres, recorded in 4.7% of tests, followed by lighting & signalling (0.9%).
Does the 2021 S-Class get worse with mileage?
Its MOT fail rate rises from 5.4% in the 0-30k band to 7.3% in the 90-120k band.
Methodology & source. Based on 1,766 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.