1991 Porsche 928 S — MOT failures & pass rate
Across 275 MOT tests, the 1991 Porsche 928 S recorded an 84.0% pass rate. Against all cars of a similar age (22.3% fail rate), the 1991 928 S comes out 6.3pp better. Failures cluster in lighting & signalling, visibility and emissions & environmental.
What the MOT record shows
Lighting & signalling dominates the failure mix at 14.5% of all tests — 8.7 points clear of visibility, so it is the first thing to check.
At component level the recurring items are headlamp aim, rear fog lamp and washers — headlamp aim alone was recorded 24 times.
Mileage matters less than usual here: the 1991 928 S fails 6.3% of the time in the 60-90k band and 9.8% at 150k+, a spread of only 3.6 points.
Advisories point at the next bill rather than this one: emissions & environmental was flagged on 18.2% of tests without failing them.
The trend is improving — the fail rate fell from 12.8% in 2021 to 10.4% in 2025, as the worst-kept examples leave the fleet.
How it compares
Top failure categories
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Lighting & signalling | 14.5% | 40 |
| 2 | Visibility | 5.8% | 16 |
| 3 | Emissions & environmental | 4.4% | 12 |
| 4 | Body, structure & corrosion | 3.6% | 10 |
| 5 | Steering | 3.3% | 9 |
| 6 | Brakes | 3.3% | 9 |
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 | 24 |
| 2 | Rear fog lamp | 15 |
| 3 | Washers | 10 |
| 4 | Stop lamp | 9 |
| 5 | Position lamp | 8 |
| 6 | Headlamp | 8 |
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 | 18.2% | 50 |
| 2 | Suspension | 14.9% | 41 |
| 3 | Other defects | 12.4% | 34 |
| 4 | Brakes | 12.0% | 33 |
| 5 | Tyres | 7.3% | 20 |
| 6 | Lighting & signalling | 7.3% | 20 |
Failure rate by mileage
Higher-mileage cars tend to fail more — often the most useful guide to real condition.
| Mileage band | Tests | Fail rate |
|---|---|---|
| 60-90k | 32 | 6.3% |
| 90-120k | 89 | 18.0% |
| 120-150k | 73 | 20.5% |
| 150k+ | 51 | 9.8% |
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2021 | 47 | 12.8% |
| 2022 | 58 | 22.4% |
| 2023 | 59 | 17.0% |
| 2024 | 63 | 15.9% |
| 2025 | 48 | 10.4% |
What to check before buying a 1991 928 S
On a 1991 928 S, lighting & signalling is what the MOT record says goes wrong most — it appeared in 14.5% of tests. Check these areas before you commit.
- Lighting & signalling (14.5% of tests): Often a cheap bulb, but persistent issues can mean wiring or corrosion in the units. Typical repair: £10–£150.
- Visibility (5.8% 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 (4.4% 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 928 Ss pass their MOT?
84.0% of the 275 1991 Porsche 928 S MOT tests in this dataset passed — a 16.0% fail rate.
What is the most common MOT failure on a 1991 Porsche 928 S?
Lighting & signalling, recorded in 14.5% of tests, followed by visibility (5.8%).
Does the 1991 928 S get worse with mileage?
Its MOT fail rate rises from 6.3% in the 60-90k band to 9.8% in the 150k+ band.
Methodology & source. Based on 275 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.