2,486 tests in 2025
Mercedes-Benz 300 reliability and MOT pass rate
81.7% passed first time. The 18.3% fail rate is 4.3 points better than the all-car average, on a median example 36 years old with 105,570 miles.
MOT pass rates / Mercedes-Benz
Pass rate
81.7%
22.6% of all cars failed; 18.3% of these did.
Fixed on the day
3.6%
Passed after a defect was put right during the visit.
Median at test
105,570 mi
36 years old.
Fail rate by age
| Age at test | Tests | Fail rate |
|---|---|---|
| 3-5 years | 6 | — |
| 6-9 years | 11 | — |
| 10-13 years | 7 | — |
| 14+ years | 2,462 | 18.4% |
What the 300 fails on
Share of failed tests with at least one fail item in each DVSA inspection section. A test can fail in several sections at once.
- Lamps, reflectors and electrical equipment8 dangerous42%
- Brakes39 dangerous36.3%
- Suspension17 dangerous33%
- Body, chassis, structure20 dangerous25.9%
- Noise, emissions and leaks4 dangerous19.3%
- Visibility18.9%
- Steering3 dangerous11.2%
- Tyres43 dangerous8.8%
Is the 300 getting worse?
The fail rate fell 0.5 points to 18.3% from 2022 to 2025 while the median one tested aged 3 years, which is about what ageing alone predicts (0 points). Read it as the fleet getting older rather than the model changing.
| Year | Tests | Median age | Fail rate | All cars | |
|---|---|---|---|---|---|
| 2022 | 3,162 | 33 | 18.8% | 22.5% | |
| 2023 | 2,927 | 33 | 20.3% | 22.8% | |
| 2024 | 2,500 | 35 | 19.3% | 23.2% | |
| 2025 | 2,482 | 36 | 18.3% | 22.6% |
Fail rate is first attempts at class 4 tests. Median age is the age of a typical 300 at its test that year, and it is the number to watch: across the whole fleet each extra year of age adds roughly 1.9 points to the fail rate, so a model whose age and fail rate rise together is simply getting older.
The exact defects that fail it
Every failure item DVSA recorded against a 300 in 2025, counted by how many tests each one appeared on.
- 1Ball joint dust cover: ball joint dust cover no longer prevents the ingress of dirt39 tests
- 2Component mounting prescribed areas: prescribed area excessively corroded significantly reducing structural strength39 tests
- 3Rear fog lamp: not working37 tests
- 4Non catalyst emissions: emissions carbon monoxide content excessive36 tests
- 5Headlamp aim: too low34 tests
- 6Position lamp: not working33 tests
- 7Washers: provides insufficient washer liquid33 tests
- 8Service brake performance: excessively binding27 tests
What wears out first
Advisories are the tester flagging wear that is still legal. A typical 300 collects 3.33 of them per test, and these are the ones that come up most. Treat it as the running-repairs list for the next year or two.
- 1Engine oil leaks: leaking excessively from engine367 tests
- 2Rigid brake pipes: excessively corroded279 tests
- 3Coil spring: corroded so that its cross sectional area is reduced and seriously weakened188 tests
- 4Condition: has a tear, caused by separation or partial failure of its structure167 tests
- 5Pins and bushes: pin or bush excessively worn125 tests
- 6Exhaust system: has a major leak of exhaust gases123 tests
- 7Wheel bearings: has excessive play108 tests
- 8Tread depth: tread depth below requirements of 1.6mm100 tests
Questions
What is the Mercedes-Benz 300 MOT pass rate?
81.7% of the 2,486 Mercedes-Benz 300 first-attempt MOTs in 2025 passed. The fail rate of 18.3% compares with 22.6% across all cars. A further 3.6% passed after a defect was fixed during the test visit.
What does a Mercedes-Benz 300 usually fail on?
The single most common failure is "Ball joint dust cover: ball joint dust cover no longer prevents the ingress of dirt", recorded on 39 failed tests, followed by "Component mounting prescribed areas: prescribed area excessively corroded significantly reducing structural strength" and "Rear fog lamp: not working". By section, lamps, reflectors and electrical equipment appears in 42% of failures, brakes appears in 36.3% of failures, suspension appears in 33% of failures.
Does age change the odds?
Sharply. At 3 to 5 years old the fail rate was 0%; at 14+ years it was 18.4%. The median Mercedes-Benz 300 tested in 2025 was 36 years old with 105,570 miles.
Is the Mercedes-Benz 300 getting less reliable?
The fail rate fell 0.5 points to 18.3% from 2022 to 2025 while the median one tested aged 3 years, which is about what ageing alone predicts (0 points). Read it as the fleet getting older rather than the model changing.
First-attempt class 4 tests, 2025, from DVSA’s anonymised MOT data (OGL v3, retrieved 2026-09-12). DVSA records newer cars trim by trim; this page adds every 300 trim together. Year-on-year figures come from the same DVSA extracts for 2026 and earlier years. Full method on the pass rates hub.
Other Mercedes-Benz models
Checking a particular 300?
The odds above are the model. The car in front of you has its own record: every test, every advisory, the mileage at each one.
Due a test? Find an approved MOT station near you.