2021 Mercedes-Benz GLS — MOT failures & pass rate
Across 643 MOT tests, the 2021 Mercedes-Benz GLS recorded an 88.3% pass rate. Against large SUVs of a similar age (8.9% fail rate), the 2021 GLS comes out 2.8pp worse. Failures cluster in tyres, brakes and lighting & signalling.
What the MOT record shows
Tyres dominates the failure mix at 8.2% of all tests — 6.4 points clear of brakes, so it is the first thing to check.
At component level the recurring items are tread depth, brake pads and headlamp aim — tread depth alone was recorded 29 times.
Mileage is the strongest signal on the record: 10.4% of 0-30k cars fail, rising to 18.7% once past 60-90k.
Advisories point at the next bill rather than this one: tyres was flagged on 19.3% of tests without failing them.
How it compares
Top failure categories
| # | Category | % of tests affected | Tests |
|---|---|---|---|
| 1 | Tyres | 8.2% | 53 |
| 2 | Brakes | 1.9% | 12 |
| 3 | Lighting & signalling | 1.4% | 9 |
| 4 | Other defects | 0.9% | 6 |
| 5 | Suspension | 0.9% | 6 |
| 6 | Visibility | 0.9% | 6 |
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 | 29 |
| 2 | Brake pads | 16 |
| 3 | Headlamp aim | 11 |
| 4 | Registration plates | 10 |
| 5 | Ball joint | 7 |
| 6 | SRS malfunction indicator lamp | 3 |
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 | 19.3% | 124 |
| 2 | Brakes | 9.6% | 62 |
| 3 | Other defects | 7.8% | 50 |
| 4 | Visibility | 4.8% | 31 |
| 5 | Suspension | 2.0% | 13 |
| 6 | Emissions & environmental | 0.6% | 4 |
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 | 251 | 10.4% |
| 30-60k | 308 | 10.7% |
| 60-90k | 75 | 18.7% |
Failure rate by age
Trend over time
| Dataset year | Tests | Fail rate |
|---|---|---|
| 2024 | 327 | 12.2% |
| 2025 | 307 | 11.1% |
What to check before buying a 2021 GLS
On a 2021 GLS, tyres is what the MOT record says goes wrong most — it appeared in 8.2% of tests. Check these areas before you commit.
- Tyres (8.2% 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.
- Brakes (1.9% of tests): Pads/discs are routine wear; binding, imbalance or corroded pipes are more serious — test for pulling under braking. Typical repair: £100–£350 per axle.
- Lighting & signalling (1.4% of tests): Often a cheap bulb, but persistent issues can mean wiring or corrosion in the units. Typical repair: £10–£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 Mercedes-Benz GLSs pass their MOT?
88.3% of the 643 2021 Mercedes-Benz GLS MOT tests in this dataset passed — a 11.7% fail rate.
What is the most common MOT failure on a 2021 Mercedes-Benz GLS?
Tyres, recorded in 8.2% of tests, followed by brakes (1.9%).
Does the 2021 GLS get worse with mileage?
Its MOT fail rate rises from 10.4% in the 0-30k band to 18.7% in the 60-90k band.
Methodology & source. Based on 643 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.