2018 Mercedes-Benz C-Class — MOT failures & pass rate
The 2018 Mercedes-Benz C-Class passed 89.6% of its 161,558 recorded MOT tests. Executive cars of a similar age fail at 10.8%, so the 2018 C-Class sits squarely on the average. Failures cluster in tyres, suspension and lighting & signalling.
What the MOT record shows
Tyres dominates the failure mix at 6.5% of all tests — 4.9 points clear of suspension, so it is the first thing to check.
At component level the recurring items are tread depth, headlamp aim and brake pads — tread depth alone was recorded 6,423 times.
Mileage matters less than usual here: the 2018 C-Class fails 7.4% of the time in the 0-30k band and 11.1% at 150k+, a spread of only 3.7 points.
Fuel type barely separates them — petrol fails 9.7% of the time against 11.0% for diesel.
Advisories point at the next bill rather than this one: tyres was flagged on 24.1% of tests without failing them.
The trend is worsening — 8.4% 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 | 6.5% | 10,536 |
| 2 | Suspension | 1.6% | 2,608 |
| 3 | Lighting & signalling | 1.5% | 2,370 |
| 4 | Emissions & environmental | 1.3% | 2,045 |
| 5 | Brakes | 1.3% | 2,031 |
| 6 | Visibility | 1.2% | 2,008 |
Most common specific failures
The exact components most often recorded as failures — more specific than the categories above.
| # | Failure item | Times recorded |
|---|---|---|
| 1 | Tread depth | 6,423 |
| 2 | Headlamp aim | 2,419 |
| 3 | Brake pads | 1,924 |
| 4 | Malfunction indicator lamp | 1,921 |
| 5 | Ball joint | 1,651 |
| 6 | Washers | 1,219 |
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 | 24.1% | 38,887 |
| 2 | Brakes | 11.5% | 18,511 |
| 3 | Other defects | 4.6% | 7,467 |
| 4 | Suspension | 3.6% | 5,825 |
| 5 | Visibility | 3.0% | 4,807 |
| 6 | Body, structure & corrosion | 0.8% | 1,264 |
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 | 53,502 | 7.4% |
| 30-60k | 74,435 | 11.1% |
| 60-90k | 25,441 | 13.6% |
| 90-120k | 6,046 | 14.0% |
| 120-150k | 1,485 | 13.1% |
| 150k+ | 620 | 11.1% |
Failure rate by age
By fuel type
| Fuel | Tests | Fail rate |
|---|---|---|
| Diesel | 83,964 | 11.0% |
| Petrol | 68,050 | 9.7% |
| Hybrid | 9,536 | 10.6% |
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2021 | 33,034 | 8.4% |
| 2022 | 32,482 | 9.0% |
| 2023 | 32,273 | 10.5% |
| 2024 | 31,914 | 11.8% |
| 2025 | 31,855 | 12.4% |
What to check before buying a 2018 C-Class
On a 2018 C-Class, tyres is what the MOT record says goes wrong most — it appeared in 6.5% of tests. Check these areas before you commit.
- Tyres (6.5% 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.
- Suspension (1.6% 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.
- 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.
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 C-Classs pass their MOT?
89.6% of the 161,558 2018 Mercedes-Benz C-Class MOT tests in this dataset passed — a 10.4% fail rate.
What is the most common MOT failure on a 2018 Mercedes-Benz C-Class?
Tyres, recorded in 6.5% of tests, followed by suspension (1.6%).
Does the 2018 C-Class get worse with mileage?
Its MOT fail rate rises from 7.4% in the 0-30k band to 11.1% in the 150k+ band.
Methodology & source. Based on 161,558 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.