65,747 tests in 2025
Mercedes-Benz B-Class reliability and MOT pass rate
77.1% passed first time. The 22.9% fail rate is 0.3 points worse than the all-car average, on a median example 11 years old with 68,191 miles.
MOT pass rates / Mercedes-Benz
Pass rate
77.1%
22.6% of all cars failed; 22.9% of these did.
Fixed on the day
4.7%
Passed after a defect was put right during the visit.
Median at test
68,191 mi
11 years old.
Fail rate by age
| Age at test | Tests | Fail rate |
|---|---|---|
| 3-5 years | 5,498 | 7.6% |
| 6-9 years | 17,861 | 14.7% |
| 10-13 years | 24,702 | 23.4% |
| 14+ years | 17,649 | 35.2% |
What the B-Class 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.
- Suspension129 dangerous41.5%
- Lamps, reflectors and electrical equipment20 dangerous30.4%
- Tyres3,970 dangerous28.3%
- Brakes1,756 dangerous24.4%
- Visibility4 dangerous12.8%
- Body, chassis, structure46 dangerous12.4%
- Noise, emissions and leaks14 dangerous11.5%
- Seat belts and supplementary restraint systems5.6%
Is the B-Class getting worse?
The fail rate rose 2.5 points to 23.3% from 2022 to 2025, against a rising rate across all cars.
| Year | Tests | Median age | Fail rate | All cars | |
|---|---|---|---|---|---|
| 2022 | 71,665 | — | 20.8% | 22.5% | |
| 2023 | 72,733 | — | 22% | 22.8% | |
| 2024 | 61,750 | — | 23.3% | 23.2% | |
| 2025 | 63,841 | — | 23.3% | 22.6% |
Fail rate is first attempts at class 4 tests. Median age is the age of a typical B-Class 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 B-Class in 2025, counted by how many tests each one appeared on.
- 1Coil spring: fractured or broken2,422 tests
- 2Linkage ball joint dust cover: ball joint dust cover no longer prevents the ingress of dirt1,603 tests
- 3Joints: constant velocity boot split or insecure, no longer prevents the ingress of dirt1,328 tests
- 4Ball joint: ball joint excessively worn1,308 tests
- 5Malfunction indicator lamp: inoperative or indicates a malfunction1,285 tests
- 6Condition: has a cut in excess of the requirements deep enough to reach the ply or cords1,183 tests
- 7Registration plate lamp(s): inoperative in the case of a single lamp or all lamps1,133 tests
- 8Brake pads: less than 1.5 mm thick1,035 tests
What wears out first
Advisories are the tester flagging wear that is still legal. A typical B-Class collects 2.46 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.
- 1Tread depth: tread depth below requirements of 1.6mm9,467 tests
- 2Condition: has a tear, caused by separation or partial failure of its structure6,545 tests
- 3Brake discs: in such a condition that it is seriously weakened5,640 tests
- 4Brake pads: less than 1.5 mm thick5,129 tests
- 5Rigid brake pipes: excessively corroded4,940 tests
- 6Brake discs: significantly and obviously worn2,532 tests
- 7Coil spring: corroded so that its cross sectional area is reduced and seriously weakened2,050 tests
- 8Ball joint: ball joint excessively worn2,031 tests
Questions
What is the Mercedes-Benz B-Class MOT pass rate?
77.1% of the 65,747 Mercedes-Benz B-Class first-attempt MOTs in 2025 passed. The fail rate of 22.9% compares with 22.6% across all cars. A further 4.7% passed after a defect was fixed during the test visit.
What does a Mercedes-Benz B-Class usually fail on?
The single most common failure is "Coil spring: fractured or broken", recorded on 2,422 failed tests, followed by "Linkage ball joint dust cover: ball joint dust cover no longer prevents the ingress of dirt" and "Joints: constant velocity boot split or insecure, no longer prevents the ingress of dirt". By section, suspension appears in 41.5% of failures, lamps, reflectors and electrical equipment appears in 30.4% of failures, tyres appears in 28.3% of failures.
Does age change the odds?
Sharply. At 3 to 5 years old the fail rate was 7.6%; at 14+ years it was 35.2%. The median Mercedes-Benz B-Class tested in 2025 was 11 years old with 68,191 miles.
Is the Mercedes-Benz B-Class getting less reliable?
The fail rate rose 2.5 points to 23.3% from 2022 to 2025, against a rising rate across all cars.
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 B-Class trim together. Year-on-year figures come from the same DVSA extracts for 2026 and earlier years. Full method on the pass rates hub.
DVSA has published 45 safety recalls naming the Mercedes-Benz B-Class: Mercedes-Benz B-Class recalls.
Other Mercedes-Benz models
Checking a particular B-Class?
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.