1989 Mercedes-Benz 420 — MOT failures & pass rate
Across 673 MOT tests, the 1989 Mercedes-Benz 420 recorded an 85.3% pass rate. Against all cars of a similar age (21.3% fail rate), the 1989 420 comes out 6.6pp better. Failures cluster in lighting & signalling, brakes and suspension.
What the MOT record shows
Lighting & signalling dominates the failure mix at 8.5% of all tests — 3.7 points clear of brakes, so it is the first thing to check.
At component level the recurring items are headlamp aim, washers and service brake performance — headlamp aim alone was recorded 37 times.
Mileage is the strongest signal on the record: 10.9% of 30-60k cars fail, rising to 23.6% once past 150k — 2.2× the risk.
Advisories point at the next bill rather than this one: suspension was flagged on 18.3% of tests without failing them.
How it compares
Top failure categories
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Lighting & signalling | 8.5% | 57 |
| 2 | Brakes | 4.8% | 32 |
| 3 | Suspension | 4.0% | 27 |
| 4 | Visibility | 4.0% | 27 |
| 5 | Body, structure & corrosion | 3.6% | 24 |
| 6 | Emissions & environmental | 2.8% | 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 | 37 |
| 2 | Washers | 21 |
| 3 | Service brake performance | 18 |
| 4 | Wipers | 13 |
| 5 | Position lamp | 12 |
| 6 | Non catalyst emissions | 11 |
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 | 18.3% | 123 |
| 2 | Emissions & environmental | 12.2% | 82 |
| 3 | Brakes | 11.9% | 80 |
| 4 | Body, structure & corrosion | 7.6% | 51 |
| 5 | Tyres | 5.5% | 37 |
| 6 | Steering | 5.2% | 35 |
Failure rate by mileage
Higher-mileage cars tend to fail more — often the most useful guide to real condition.
| Mileage band | Tests | Fail rate |
|---|---|---|
| 30-60k | 101 | 10.9% |
| 60-90k | 169 | 13.6% |
| 90-120k | 196 | 12.2% |
| 120-150k | 118 | 19.5% |
| 150k+ | 72 | 23.6% |
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2021 | 139 | 15.8% |
| 2022 | 145 | 15.2% |
| 2023 | 126 | 13.5% |
| 2024 | 128 | 14.1% |
| 2025 | 135 | 14.8% |
What to check before buying a 1989 420
On a 1989 420, lighting & signalling is what the MOT record says goes wrong most — it appeared in 8.5% of tests. Check these areas before you commit.
- Lighting & signalling (8.5% of tests): Often a cheap bulb, but persistent issues can mean wiring or corrosion in the units. Typical repair: £10–£150.
- Brakes (4.8% 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.
- Suspension (4.0% 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 1989 Mercedes-Benz 420s pass their MOT?
85.3% of the 673 1989 Mercedes-Benz 420 MOT tests in this dataset passed — a 14.7% fail rate.
What is the most common MOT failure on a 1989 Mercedes-Benz 420?
Lighting & signalling, recorded in 8.5% of tests, followed by brakes (4.8%).
Does the 1989 420 get worse with mileage?
Its MOT fail rate rises from 10.9% in the 30-60k band to 23.6% in the 150k+ band.
Methodology & source. Based on 673 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.