2021 BMW 4 Series — MOT failures & pass rate
The 2021 BMW 4 Series passed 90.2% of its 15,529 recorded MOT tests. Against coupes & convertibles of a similar age (7.9% fail rate), the 2021 4 Series comes out 1.9pp worse. Failures cluster in tyres, lighting & signalling and visibility.
What the MOT record shows
Tyres dominates the failure mix at 8.0% of all tests — 6.7 points clear of lighting & signalling, so it is the first thing to check.
At component level the recurring items are tread depth, headlamp aim and registration plates — tread depth alone was recorded 325 times.
Mileage matters less than usual here: the 2021 4 Series fails 8.6% of the time in the 0-30k band and 10.4% at 90-120k, a spread of only 1.8 points.
Split by fuel, diesel examples fail 2.6pp more often than petrol ones (11.6% vs 9.1%) — worth weighing if you have a choice.
Advisories point at the next bill rather than this one: tyres was flagged on 15.2% of tests without failing them.
The trend is worsening — 4.6% of tests failed in 2023 against 9.5% in 2025, the usual pattern as a fleet ages.
How it compares
Top failure categories
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Tyres | 8.0% | 1,239 |
| 2 | Lighting & signalling | 1.3% | 200 |
| 3 | Visibility | 0.8% | 126 |
| 4 | Brakes | 0.4% | 67 |
| 5 | Other defects | 0.4% | 61 |
| 6 | Road wheels | 0.3% | 53 |
Most common specific failures
The exact components most often recorded as failures — more specific than the categories above.
| # | Failure item | Times recorded |
|---|---|---|
| 1 | Tread depth | 325 |
| 2 | Headlamp aim | 186 |
| 3 | Registration plates | 98 |
| 4 | Washers | 87 |
| 5 | Brake pads | 54 |
| 6 | Side repeaters | 51 |
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 | 15.2% | 2,355 |
| 2 | Brakes | 3.6% | 554 |
| 3 | Other defects | 2.9% | 457 |
| 4 | Suspension | 1.7% | 267 |
| 5 | Visibility | 1.7% | 262 |
| 6 | Road wheels | 0.8% | 117 |
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 | 9,136 | 8.6% |
| 30-60k | 5,745 | 11.3% |
| 60-90k | 594 | 14.3% |
| 90-120k | 48 | 10.4% |
Failure rate by age
By fuel type
| Fuel | Tests | Fail rate |
|---|---|---|
| Petrol | 9,300 | 9.1% |
| Diesel | 4,039 | 11.6% |
| Hybrid | 2,189 | 9.6% |
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2023 | 410 | 4.6% |
| 2024 | 7,576 | 10.3% |
| 2025 | 7,533 | 9.5% |
What to check before buying a 2021 4 Series
On a 2021 4 Series, tyres is what the MOT record says goes wrong most — it appeared in 8.0% of tests. Check these areas before you commit.
- Tyres (8.0% 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 (1.3% of tests): Often a cheap bulb, but persistent issues can mean wiring or corrosion in the units. Typical repair: £10–£150.
- Visibility (0.8% 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.
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 BMW 4 Seriess pass their MOT?
90.2% of the 15,529 2021 BMW 4 Series MOT tests in this dataset passed — a 9.8% fail rate.
What is the most common MOT failure on a 2021 BMW 4 Series?
Tyres, recorded in 8.0% of tests, followed by lighting & signalling (1.3%).
Does the 2021 4 Series get worse with mileage?
Its MOT fail rate rises from 8.6% in the 0-30k band to 10.4% in the 90-120k band.
Methodology & source. Based on 15,529 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.