1998 Porsche 911 — MOT failures & pass rate
5,863 MOT tests on the 1998 Porsche 911 are in this dataset, and 85.1% of them passed. That is 6.6 percentage points better than coupes & convertibles of a similar age, which fail at 21.6%. Failures cluster in lighting & signalling, brakes and emissions & environmental.
What the MOT record shows
One area stands out: lighting & signalling, recorded in 8.8% of tests against 4.9% for the next-worst category.
At component level the recurring items are catalyst emissions, headlamp aim and rigid brake pipes — catalyst emissions alone was recorded 234 times.
A 150k+ example is materially riskier than a 0-30k one: 22.3% versus 7.2%.
Brakes is the most common advisory, noted on 23.4% of tests — work that passed today but is likely due soon.
How it compares
Top failure categories
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Lighting & signalling | 8.8% | 518 |
| 2 | Brakes | 4.9% | 285 |
| 3 | Emissions & environmental | 3.7% | 218 |
| 4 | Suspension | 3.5% | 205 |
| 5 | Visibility | 2.5% | 148 |
| 6 | Tyres | 2.4% | 139 |
Most common specific failures
The exact components most often recorded as failures — more specific than the categories above.
| # | Failure item | Times recorded |
|---|---|---|
| 1 | Catalyst emissions | 234 |
| 2 | Headlamp aim | 225 |
| 3 | Rigid brake pipes | 172 |
| 4 | Headlamp | 149 |
| 5 | Position lamp | 113 |
| 6 | Rbt (sp) | 111 |
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 | 23.4% | 1,370 |
| 2 | Suspension | 15.1% | 884 |
| 3 | Tyres | 14.9% | 871 |
| 4 | Emissions & environmental | 10.1% | 592 |
| 5 | Lighting & signalling | 7.4% | 432 |
| 6 | Other defects | 4.3% | 254 |
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 | 221 | 7.2% |
| 30-60k | 667 | 8.8% |
| 60-90k | 1,544 | 13.2% |
| 90-120k | 1,884 | 15.1% |
| 120-150k | 1,098 | 19.2% |
| 150k+ | 440 | 22.3% |
Failure rate by age
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2021 | 1,295 | 14.9% |
| 2022 | 1,239 | 15.7% |
| 2023 | 1,157 | 15.6% |
| 2024 | 1,126 | 14.0% |
| 2025 | 1,046 | 14.1% |
What to check before buying a 1998 911
The failure pattern for this year is specific enough to inspect against: lighting & signalling accounted for 8.8% of tests. Start there.
- Lighting & signalling (8.8% of tests): Often a cheap bulb, but persistent issues can mean wiring or corrosion in the units. Typical repair: £10–£150.
- Brakes (4.9% 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.
- Emissions & environmental (3.7% of tests): More common on older diesels (DPF/EGR) — can be expensive; check for warning lights and smoke. Typical repair: £100–£600.
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 1998 Porsche 911s pass their MOT?
85.1% of the 5,863 1998 Porsche 911 MOT tests in this dataset passed — a 14.9% fail rate.
What is the most common MOT failure on a 1998 Porsche 911?
Lighting & signalling, recorded in 8.8% of tests, followed by brakes (4.9%).
Does the 1998 911 get worse with mileage?
Its MOT fail rate rises from 7.2% in the 0-30k band to 22.3% in the 150k+ band.
Methodology & source. Based on 5,863 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.