2021 Audi S4 — MOT failures & pass rate
Across 327 MOT tests, the 2021 Audi S4 recorded a 93.0% pass rate. Against executive cars of a similar age (9.7% fail rate), the 2021 S4 comes out 2.7pp better. Failures cluster in tyres, lighting & signalling and suspension.
What the MOT record shows
Tyres dominates the failure mix at 6.4% of all tests — 4.9 points clear of lighting & signalling, so it is the first thing to check.
At component level the recurring items are headlamp aim, mounting and tread depth — headlamp aim alone was recorded 6 times.
Advisories point at the next bill rather than this one: tyres was flagged on 21.1% of tests without failing them.
How it compares
Top failure categories
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Tyres | 6.4% | 21 |
| 2 | Lighting & signalling | 1.5% | 5 |
| 3 | Suspension | 0.9% | 3 |
| 4 | Visibility | 0.3% | 1 |
| 5 | Brakes | 0.3% | 1 |
| 6 | Emissions & environmental | 0.3% | 1 |
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 | 6 |
| 2 | Mounting | 3 |
| 3 | Tread depth | 2 |
| 4 | Washers | 1 |
| 5 | Malfunction indicator lamp | 1 |
| 6 | SRS malfunction indicator lamp | 1 |
Top advisory categories
Advisories aren't failures, but they flag work likely needed soon — useful when budgeting.
| # | Category | % of tests with advisory | Tests |
|---|---|---|---|
| 1 | Tyres | 21.1% | 69 |
| 2 | Brakes | 8.9% | 29 |
| 3 | Suspension | 6.1% | 20 |
| 4 | Other defects | 4.3% | 14 |
| 5 | Visibility | 3.1% | 10 |
| 6 | Lighting & signalling | 0.3% | 1 |
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 | 121 | 6.6% |
| 30-60k | 170 | 7.1% |
Failure rate by age
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2024 | 154 | 5.2% |
| 2025 | 157 | 8.9% |
What to check before buying a 2021 S4
On a 2021 S4, tyres is what the MOT record says goes wrong most — it appeared in 6.4% of tests. Check these areas before you commit.
- Tyres (6.4% of tests): Usually a quick, known-cost fix, but check tread, age and uneven wear (which can hint at alignment or suspension issues). Typical repair: £50–£120 per tyre.
- Lighting & signalling (1.5% of tests): Often a cheap bulb, but persistent issues can mean wiring or corrosion in the units. Typical repair: £10–£150.
- Suspension (0.9% 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 2021 Audi S4s pass their MOT?
93.0% of the 327 2021 Audi S4 MOT tests in this dataset passed — a 7.0% fail rate.
What is the most common MOT failure on a 2021 Audi S4?
Tyres, recorded in 6.4% of tests, followed by lighting & signalling (1.5%).
Does the 2021 S4 get worse with mileage?
Its MOT fail rate rises from 6.6% in the 0-30k band to 7.1% in the 30-60k band.
Methodology & source. Based on 327 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.