1991 Porsche 911 — MOT failures & pass rate
Across 1,531 MOT tests, the 1991 Porsche 911 recorded an 89.6% pass rate. Coupes & convertibles of a similar age fail 18.7% of the time, so this is 8.3pp better than the group it competes with. Failures cluster in lighting & signalling, visibility and emissions & environmental.
What the MOT record shows
Lighting & signalling dominates the failure mix at 8.4% of all tests — 5.5 points clear of visibility, so it is the first thing to check.
At component level the recurring items are headlamp aim, washers and position lamp — headlamp aim alone was recorded 107 times.
Condition tracks the odometer closely. Failures run at 5.7% in the 0-30k band and 15.9% in the 150k+ band, a 10.3-point spread — more than double.
Advisories point at the next bill rather than this one: emissions & environmental was flagged on 12.1% of tests without failing them.
The trend is improving — the fail rate fell from 11.5% in 2021 to 7.4% in 2025, as the worst-kept examples leave the fleet.
How it compares
Top failure categories
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Lighting & signalling | 8.4% | 128 |
| 2 | Visibility | 2.8% | 43 |
| 3 | Emissions & environmental | 2.2% | 33 |
| 4 | Brakes | 2.0% | 31 |
| 5 | Suspension | 1.9% | 29 |
| 6 | Body, structure & corrosion | 1.2% | 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 | 107 |
| 2 | Washers | 36 |
| 3 | Position lamp | 22 |
| 4 | Rear fog lamp | 18 |
| 5 | Catalyst emissions | 18 |
| 6 | Registration plate lamp(s) | 18 |
Top advisory categories
Advisories aren't failures, but they flag work likely needed soon — useful when budgeting.
| # | Category | % of tests with advisory | Tests |
|---|---|---|---|
| 1 | Emissions & environmental | 12.1% | 185 |
| 2 | Tyres | 9.4% | 144 |
| 3 | Brakes | 5.9% | 90 |
| 4 | Suspension | 5.4% | 82 |
| 5 | Lighting & signalling | 4.3% | 65 |
| 6 | Other defects | 2.9% | 44 |
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 | 159 | 5.7% |
| 30-60k | 216 | 9.3% |
| 60-90k | 378 | 9.5% |
| 90-120k | 463 | 9.1% |
| 120-150k | 226 | 16.8% |
| 150k+ | 88 | 15.9% |
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2021 | 260 | 11.5% |
| 2022 | 345 | 13.0% |
| 2023 | 308 | 11.4% |
| 2024 | 319 | 8.5% |
| 2025 | 299 | 7.4% |
What to check before buying a 1991 911
On a 1991 911, lighting & signalling is what the MOT record says goes wrong most — it appeared in 8.4% of tests. Check these areas before you commit.
- Lighting & signalling (8.4% of tests): Often a cheap bulb, but persistent issues can mean wiring or corrosion in the units. Typical repair: £10–£150.
- Visibility (2.8% 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.
- Emissions & environmental (2.2% 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 1991 Porsche 911s pass their MOT?
89.6% of the 1,531 1991 Porsche 911 MOT tests in this dataset passed — a 10.4% fail rate.
What is the most common MOT failure on a 1991 Porsche 911?
Lighting & signalling, recorded in 8.4% of tests, followed by visibility (2.8%).
Does the 1991 911 get worse with mileage?
Its MOT fail rate rises from 5.7% in the 0-30k band to 15.9% in the 150k+ band.
Methodology & source. Based on 1,531 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.