1988 Mercedes-Benz 420 — MOT failures & pass rate
The 1988 Mercedes-Benz 420 passed 84.4% of its 870 recorded MOT tests. All cars of a similar age fail 20.9% of the time, so this is 5.3pp better than the group it competes with. Failures cluster in lighting & signalling, visibility and brakes.
What the MOT record shows
One area stands out: lighting & signalling, recorded in 10.3% of tests against 5.9% for the next-worst category.
At component level the recurring items are headlamp aim, ball joint dust cover and wipers — headlamp aim alone was recorded 55 times.
A 150k+ example is materially riskier than a 0-30k one: 21.7% versus 5.7%.
Suspension is the most common advisory, noted on 21.9% of tests — work that passed today but is likely due soon.
The trend is improving — the fail rate fell from 17.8% in 2021 to 13.2% in 2025, as the worst-kept examples leave the fleet.
How it compares
Top failure categories
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Lighting & signalling | 10.3% | 90 |
| 2 | Visibility | 5.9% | 51 |
| 3 | Brakes | 5.6% | 49 |
| 4 | Suspension | 5.2% | 45 |
| 5 | Emissions & environmental | 3.3% | 29 |
| 6 | Body, structure & corrosion | 2.2% | 19 |
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 | 55 |
| 2 | Ball joint dust cover | 38 |
| 3 | Wipers | 34 |
| 4 | Service brake performance | 34 |
| 5 | Washers | 30 |
| 6 | Non catalyst emissions | 25 |
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 | 21.9% | 191 |
| 2 | Brakes | 19.5% | 170 |
| 3 | Emissions & environmental | 14.2% | 124 |
| 4 | Tyres | 12.9% | 112 |
| 5 | Body, structure & corrosion | 10.0% | 87 |
| 6 | Steering | 8.3% | 72 |
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 | 35 | 5.7% |
| 30-60k | 110 | 7.3% |
| 60-90k | 237 | 15.6% |
| 90-120k | 220 | 18.6% |
| 120-150k | 152 | 14.5% |
| 150k+ | 115 | 21.7% |
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2021 | 174 | 17.8% |
| 2022 | 183 | 19.1% |
| 2023 | 174 | 12.6% |
| 2024 | 172 | 15.1% |
| 2025 | 167 | 13.2% |
What to check before buying a 1988 420
The failure pattern for this year is specific enough to inspect against: lighting & signalling accounted for 10.3% of tests. Start there.
- Lighting & signalling (10.3% of tests): Often a cheap bulb, but persistent issues can mean wiring or corrosion in the units. Typical repair: £10–£150.
- Visibility (5.9% of tests): Wipers, washers, mirrors and screen damage — usually inexpensive, but check for chips in the driver's line of sight. Typical repair: £15–£150.
- Brakes (5.6% 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 1988 Mercedes-Benz 420s pass their MOT?
84.4% of the 870 1988 Mercedes-Benz 420 MOT tests in this dataset passed — a 15.6% fail rate.
What is the most common MOT failure on a 1988 Mercedes-Benz 420?
Lighting & signalling, recorded in 10.3% of tests, followed by visibility (5.9%).
Does the 1988 420 get worse with mileage?
Its MOT fail rate rises from 5.7% in the 0-30k band to 21.7% in the 150k+ band.
Methodology & source. Based on 870 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.