3,577 tests in 2025
MG B reliability and MOT pass rate
84.6% passed first time. The 15.4% fail rate is 7.2 points better than the all-car average, on a median example 52 years old with 41,652 miles.
Pass rate
84.6%
22.6% of all cars failed; 15.4% of these did.
Fixed on the day
2.2%
Passed after a defect was put right during the visit.
Median at test
41,652 mi
52 years old.
Fail rate by age
| Age at test | Tests | Fail rate |
|---|---|---|
| 3-5 years | 1 | — |
| 6-9 years | 3 | — |
| 10-13 years | 5 | — |
| 14+ years | 3,568 | 15.5% |
What the B 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 equipment47 dangerous45.5%
- Brakes48 dangerous36.8%
- Visibility1 dangerous24.1%
- Suspension13 dangerous20.5%
- Noise, emissions and leaks1 dangerous19%
- Steering9 dangerous17%
- Body, chassis, structure20 dangerous14.5%
- Seat belts and supplementary restraint systems2 dangerous3.6%
Is the B getting worse?
The fail rate fell 2.4 points to 15.4% from 2022 to 2025, against a rising rate across all cars.
| Year | Tests | Median age | Fail rate | All cars | |
|---|---|---|---|---|---|
| 2022 | 4,469 | — | 17.8% | 22.5% | |
| 2023 | 4,089 | — | 18.9% | 22.8% | |
| 2024 | 3,099 | — | 15.8% | 23.2% | |
| 2025 | 3,396 | — | 15.4% | 22.6% |
Fail rate is first attempts at class 4 tests. Median age is the age of a typical B 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 in 2025, counted by how many tests each one appeared on.
- 1Non catalyst emissions: emissions carbon monoxide content excessive71 tests
- 2Washers: not working70 tests
- 3Service brake imbalance: across an axle64 tests
- 4Steering rack: gaiter missing or no longer prevents the ingress of dirt53 tests
- 5Position lamp: not working53 tests
- 6Service brake performance: excessively binding51 tests
- 7Horn: not working47 tests
- 8Stop lamp: all not working43 tests
What wears out first
Advisories are the tester flagging wear that is still legal. A typical B collects 2.39 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 engine437 tests
- 2Pins and bushes: pin or bush excessively worn158 tests
- 3Wheel bearings: has excessive play155 tests
- 4Transmission oil leaks: leaking excessively from transmission142 tests
- 5Service brake performance: excessively binding85 tests
- 6Non-component advisories: Play in steering rack inner joint(s)83 tests
- 7Condition: has a tear, caused by separation or partial failure of its structure73 tests
- 8Shock absorbers: has a serious fluid leak70 tests
Questions
What is the MG B MOT pass rate?
84.6% of the 3,577 MG B first-attempt MOTs in 2025 passed. The fail rate of 15.4% compares with 22.6% across all cars. A further 2.2% passed after a defect was fixed during the test visit.
What does a MG B usually fail on?
The single most common failure is "Non catalyst emissions: emissions carbon monoxide content excessive", recorded on 71 failed tests, followed by "Washers: not working" and "Service brake imbalance: across an axle". By section, lamps, reflectors and electrical equipment appears in 45.5% of failures, brakes appears in 36.8% of failures, visibility appears in 24.1% of failures.
Does age change the odds?
Sharply. At 3 to 5 years old the fail rate was 0%; at 14+ years it was 15.5%. The median MG B tested in 2025 was 52 years old with 41,652 miles.
Is the MG B getting less reliable?
The fail rate fell 2.4 points to 15.4% 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 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 MG models
Checking a particular B?
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.