1991 Mercedes-Benz 500 — MOT failures & pass rate
720 MOT tests on the 1991 Mercedes-Benz 500 are in this dataset, and 86.8% of them passed. Against all cars of a similar age (22.3% fail rate), the 1991 500 comes out 9.1pp better. Failures cluster in lighting & signalling, brakes and suspension.
What the MOT record shows
No single area dominates — lighting & signalling (7.1%) and brakes (4.2%) are close, so failures are spread across several systems rather than one weak point.
At component level the recurring items are headlamp aim, ball joint dust cover and service brake performance — headlamp aim alone was recorded 21 times.
Mileage is the strongest signal on the record: 0.0% of 0-30k cars fail, rising to 16.7% once past 150k — 166.7× the risk.
Advisories point at the next bill rather than this one: suspension was flagged on 21.3% of tests without failing them.
The trend is improving — the fail rate fell from 14.1% in 2021 to 11.5% in 2025, as the worst-kept examples leave the fleet.
How it compares
Top failure categories
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Lighting & signalling | 7.1% | 51 |
| 2 | Brakes | 4.2% | 30 |
| 3 | Suspension | 4.2% | 30 |
| 4 | Emissions & environmental | 3.1% | 22 |
| 5 | Visibility | 2.4% | 17 |
| 6 | Tyres | 1.9% | 14 |
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 | 21 |
| 2 | Ball joint dust cover | 18 |
| 3 | Service brake performance | 17 |
| 4 | Position lamp | 16 |
| 5 | Wipers | 13 |
| 6 | Rigid brake pipes | 12 |
Top advisory categories
Advisories aren't failures, but they flag work likely needed soon — useful when budgeting.
| # | Category | % of tests with advisory | Tests |
|---|---|---|---|
| 1 | Suspension | 21.3% | 153 |
| 2 | Brakes | 20.3% | 146 |
| 3 | Emissions & environmental | 14.3% | 103 |
| 4 | Tyres | 13.5% | 97 |
| 5 | Steering | 11.9% | 86 |
| 6 | Other defects | 6.4% | 46 |
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 | 34 | 0.0% |
| 30-60k | 78 | 6.4% |
| 60-90k | 212 | 13.2% |
| 90-120k | 212 | 14.6% |
| 120-150k | 123 | 17.1% |
| 150k+ | 60 | 16.7% |
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2021 | 156 | 14.1% |
| 2022 | 153 | 10.5% |
| 2023 | 157 | 15.9% |
| 2024 | 124 | 13.7% |
| 2025 | 130 | 11.5% |
What to check before buying a 1991 500
On a 1991 500, lighting & signalling is what the MOT record says goes wrong most — it appeared in 7.1% of tests. Check these areas before you commit.
- Lighting & signalling (7.1% of tests): Often a cheap bulb, but persistent issues can mean wiring or corrosion in the units. Typical repair: £10–£150.
- Brakes (4.2% 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.
- Suspension (4.2% 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 1991 Mercedes-Benz 500s pass their MOT?
86.8% of the 720 1991 Mercedes-Benz 500 MOT tests in this dataset passed — a 13.2% fail rate.
What is the most common MOT failure on a 1991 Mercedes-Benz 500?
Lighting & signalling, recorded in 7.1% of tests, followed by brakes (4.2%).
Does the 1991 500 get worse with mileage?
Its MOT fail rate rises from 0.0% in the 0-30k band to 16.7% in the 150k+ band.
Methodology & source. Based on 720 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.