1999 Audi S4 — MOT failures & pass rate
The 1999 Audi S4 passed 82.9% of its 316 recorded MOT tests. Executive cars of a similar age fail 23.2% of the time, so this is 6.1pp better than the group it competes with. Failures cluster in lighting & signalling, emissions & environmental and suspension.
What the MOT record shows
One area stands out: lighting & signalling, recorded in 10.1% of tests against 7.0% for the next-worst category.
At component level the recurring items are catalyst emissions, headlamp aim and ball joint — catalyst emissions alone was recorded 34 times.
Mileage is the strongest signal on the record: 11.4% of 90-120k cars fail, rising to 20.4% once past 150k.
Brakes is the most common advisory, noted on 23.4% of tests — work that passed today but is likely due soon.
The trend is improving — the fail rate fell from 22.5% 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 | 10.1% | 32 |
| 2 | Emissions & environmental | 7.0% | 22 |
| 3 | Suspension | 5.4% | 17 |
| 4 | Brakes | 4.8% | 15 |
| 5 | Body, structure & corrosion | 4.8% | 15 |
| 6 | Steering | 3.8% | 12 |
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 | 34 |
| 2 | Headlamp aim | 16 |
| 3 | Ball joint | 14 |
| 4 | Side repeaters | 14 |
| 5 | Joints | 12 |
| 6 | Anti-lock braking system | 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 | Brakes | 23.4% | 74 |
| 2 | Suspension | 23.1% | 73 |
| 3 | Tyres | 15.8% | 50 |
| 4 | Emissions & environmental | 13.6% | 43 |
| 5 | Body, structure & corrosion | 12.7% | 40 |
| 6 | Lighting & signalling | 8.5% | 27 |
Failure rate by mileage
Higher-mileage cars tend to fail more — often the most useful guide to real condition.
| Mileage band | Tests | Fail rate |
|---|---|---|
| 90-120k | 44 | 11.4% |
| 120-150k | 69 | 15.9% |
| 150k+ | 176 | 20.4% |
Failure rate by age
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2021 | 71 | 22.5% |
| 2022 | 70 | 21.4% |
| 2023 | 71 | 16.9% |
| 2024 | 56 | 10.7% |
| 2025 | 48 | 10.4% |
What to check before buying a 1999 S4
The failure pattern for this year is specific enough to inspect against: lighting & signalling accounted for 10.1% of tests. Start there.
- Lighting & signalling (10.1% of tests): Often a cheap bulb, but persistent issues can mean wiring or corrosion in the units. Typical repair: £10–£150.
- Emissions & environmental (7.0% of tests): More common on older diesels (DPF/EGR) — can be expensive; check for warning lights and smoke. Typical repair: £100–£600.
- Suspension (5.4% 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 1999 Audi S4s pass their MOT?
82.9% of the 316 1999 Audi S4 MOT tests in this dataset passed — a 17.1% fail rate.
What is the most common MOT failure on a 1999 Audi S4?
Lighting & signalling, recorded in 10.1% of tests, followed by emissions & environmental (7.0%).
Does the 1999 S4 get worse with mileage?
Its MOT fail rate rises from 11.4% in the 90-120k band to 20.4% in the 150k+ band.
Methodology & source. Based on 316 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.