2004 Mercedes-Benz SLK — MOT failures & pass rate
The 2004 Mercedes-Benz SLK passed 75.8% of its 19,843 recorded MOT tests. Coupes & convertibles of a similar age fail 22.4% of the time, so this is 1.8pp worse than the group it competes with. Failures cluster in suspension, lighting & signalling and brakes.
What the MOT record shows
No single area dominates — suspension (12.6%) and lighting & signalling (9.6%) are close, so failures are spread across several systems rather than one weak point.
At component level the recurring items are coil spring, headlamp aim and ball joint — coil spring alone was recorded 1,297 times.
Mileage is the strongest signal on the record: 11.1% of 0-30k cars fail, rising to 29.5% once past 150k — 2.7× the risk.
Brakes is the most common advisory, noted on 29.7% of tests — work that passed today but is likely due soon.
How it compares
Top failure categories
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Suspension | 12.6% | 2,496 |
| 2 | Lighting & signalling | 9.6% | 1,913 |
| 3 | Brakes | 7.0% | 1,388 |
| 4 | Tyres | 4.2% | 830 |
| 5 | Emissions & environmental | 3.6% | 725 |
| 6 | Steering | 3.6% | 712 |
Most common specific failures
The exact components most often recorded as failures — more specific than the categories above.
| # | Failure item | Times recorded |
|---|---|---|
| 1 | Coil spring | 1,297 |
| 2 | Headlamp aim | 956 |
| 3 | Ball joint | 752 |
| 4 | Rigid brake pipes | 666 |
| 5 | Headlamp | 645 |
| 6 | Steering rack | 559 |
Top advisory categories
Advisories aren't failures, but they flag work likely needed soon — useful when budgeting.
| # | Category | % of tests with advisory | Tests |
|---|---|---|---|
| 1 | Brakes | 29.7% | 5,891 |
| 2 | Suspension | 24.3% | 4,812 |
| 3 | Tyres | 22.5% | 4,468 |
| 4 | Lighting & signalling | 11.6% | 2,301 |
| 5 | Other defects | 8.0% | 1,587 |
| 6 | Body, structure & corrosion | 7.8% | 1,557 |
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 | 760 | 11.1% |
| 30-60k | 4,103 | 18.8% |
| 60-90k | 7,390 | 24.2% |
| 90-120k | 5,306 | 27.8% |
| 120-150k | 1,804 | 30.1% |
| 150k+ | 454 | 29.5% |
Failure rate by age
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2021 | 4,413 | 24.4% |
| 2022 | 4,246 | 24.3% |
| 2023 | 4,040 | 24.5% |
| 2024 | 3,756 | 24.4% |
| 2025 | 3,388 | 23.5% |
What to check before buying a 2004 SLK
The failure pattern for this year is specific enough to inspect against: suspension accounted for 12.6% of tests. Start there.
- Suspension (12.6% 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 (9.6% of tests): Often a cheap bulb, but persistent issues can mean wiring or corrosion in the units. Typical repair: £10–£150.
- Brakes (7.0% 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 2004 Mercedes-Benz SLKs pass their MOT?
75.8% of the 19,843 2004 Mercedes-Benz SLK MOT tests in this dataset passed — a 24.2% fail rate.
What is the most common MOT failure on a 2004 Mercedes-Benz SLK?
Suspension, recorded in 12.6% of tests, followed by lighting & signalling (9.6%).
Does the 2004 SLK get worse with mileage?
Its MOT fail rate rises from 11.1% in the 0-30k band to 29.5% in the 150k+ band.
Methodology & source. Based on 19,843 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.