2025 MOT results
Mercedes-Benz B-Class common problems
The most common reason a Mercedes-Benz B-Class fails its MOT is a broken coil spring, on 13.4% of its 19,455 failed tests in 2025. Against other cars of the same age, 3 faults stand out: a split joint boot at 8.9% of failures against 3.2% expected; a number plate lamp out at 7.2% of failures against 3.8% expected; the engine management light on at 9.2% of failures against 5.2% expected.
- Tests in 2025 71,047 Cars aged three and over
- Failed first time 27.4% 19,455 tests
- Found a dangerous defect 7.2% Unsafe to drive away
- Ended with an advisory 49.0% A problem to watch, not a failure
What fails a Mercedes-Benz B-Class MOT
Each bar is the share of failed Mercedes-Benz B-Class tests with that defect. Where we can compare it with cars of the same registration years, the marker shows what an average car of those ages records (12 of the 12 items below).
Most common reasons for failure
A test can fail for more than one defect, so shares add up to more than 100%.
| Defect | Share of failed tests |
|---|---|
| Coil spring: fractured or broken Suspension | 13.4% |
| Malfunction indicator lamp: inoperative or indicates a malfunction Noise, emissions and leaks | 9.2% |
| Linkage ball joint dust cover no longer prevents the ingress of dirt Suspension | 8.9% |
| Drive shafts: constant velocity boot split or insecure, no longer prevents the ingress of dirt Body, chassis, structure | 7.4% |
| Registration plate lamp(s): inoperative in the case of a single lamp or all lamps Lamps, reflectors and electrical equipment | 7.2% |
| Tyres: cut in excess of the requirements deep enough to reach the ply or cords Tyres | 6.6% |
| Suspension arms: ball joint excessively worn Suspension | 6.5% |
| Brake pads: less than 1.5 mm thick Brakes | 5.9% |
| Tyres: ply or cords exposed Tyres | 5.7% |
| Washers: provides insufficient washer liquid Visibility | 5.5% |
| Tyres: tread depth below requirements of 1.6mm Tyres | 5.5% |
| Stop lamp: not working Lamps, reflectors and electrical equipment | 4.9% |
Source:DVSA,UK Motoring analysis 2025 Updated
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Broken coil spring
13.4% of failures 9.9% expected somewhat more often
A broken suspension spring, which usually snaps in the bottom coil and often fails on both sides within a year.
Look at each corner for a sagging ride height, and listen for a knock over speed bumps.
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Engine management light on
9.2% of failures 5.2% expected 1.8 times as often
The engine management light is on, or has been disconnected. Either fails the test.
A cheap code reader on the diagnostic socket will say what the car has stored before you pay for a test.
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Split joint boot
8.9% of failures 3.2% expected 2.8 times as often
A split rubber boot on a joint or driveshaft. The joint may still be sound, but dirt and water get in once the boot is open.
Turn the wheels to full lock and look behind them for greasy splits in the rubber concertina.
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Split joint boot
7.4% of failures 4.7% expected 1.6 times as often
A split rubber boot on a joint or driveshaft. The joint may still be sound, but dirt and water get in once the boot is open.
Turn the wheels to full lock and look behind them for greasy splits in the rubber concertina.
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Number plate lamp out
7.2% of failures 3.8% expected 1.9 times as often
The lamp over the rear number plate not working, so the plate cannot be read at night.
Walk round the car with the lights on and the hazards going; these are the cheapest failures to avoid.
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Cut tyre
6.6% of failures 4.5% expected 1.5 times as often
A cut in the tyre deep or long enough to reach the structure underneath, usually from a kerb or debris.
Run a hand round the inner and outer walls of each tyre, which is where kerbing shows.
Which parts of the car fail
Lamps, reflectors and electrical equipment is the area that most often fails a Mercedes-Benz B-Class, on 35.7% of failed tests. The widest gap against cars of the same registration years is tyres, on 24.8% against 22.2% expected.
Failure categories
DVSA's own sections of the test. The marker is what cars of the same registration years record.
| Defect category | Share of failed tests |
|---|---|
| Lamps, reflectors and electrical equipment | 35.7% |
| Suspension | 34.8% |
| Tyres | 24.8% |
| Brakes | 20.8% |
| Visibility | 14.2% |
| Noise, emissions and leaks | 11.7% |
| Body, chassis, structure | 10.6% |
| Seat belts and supplementary restraint systems | 5.2% |
Source:DVSA,UK Motoring analysis 2025 Updated
What testers warn about
49.0% of Mercedes-Benz B-Class tests ended with at least one advisory: a fault the tester found that did not fail the test. On Mercedes-Benz B-Classes, these are the items to ask about on a car you are viewing, because they are what the last tester expected to go next.
Most common advisories
Share of all tests, passes included.
| Advisory | Share of tests |
|---|---|
| Tread depth: worn close to legal limit or worn on edge Tyres | 16.4% |
| Tyres: slightly damaged or cracking or perishing Tyres | 10.0% |
| Brake discs: worn, pitted or scored, but not seriously weakened Brakes | 8.5% |
| Brake pads: wearing thin Brakes | 7.8% |
| Rigid brake pipes: corroded, covered in grease or other material Brakes | 7.5% |
| Brake discs: worn, but not excessively Brakes | 3.9% |
| Coil spring: corroded Suspension | 3.1% |
| Suspension arms: ball joint has slight play Suspension | 2.8% |
| Tyres: cut but not deep enough to reach the ply or cords Tyres | 2.5% |
| Registration plates: deteriorated but not likely to be misread Identification of the vehicle | 2.4% |
| Child seat fitted not allowing full inspection of adult belt Non-component advisories | 2.2% |
| Shock absorbers: light misting of oil Suspension | 1.8% |
Source:DVSA,UK Motoring analysis 2025 Updated
What changes as a Mercedes-Benz B-Class gets older
A 2020 Mercedes-Benz B-Class failed 10.0% of its MOT tests in 2025; a 2007 one failed 44.4%. What fails changes as much as how often, and these are the two years themselves rather than an average across them.
2020 Mercedes-Benz B-Class 10.0% failed, from 2,923 tests
- Cut tyre 21.3%
- Worn brake pads 10.3%
- Tyre worn through to the cords 9.3%
- Headlamp aim set too low 7.2%
- Tyre worn below the legal limit 6.5%
- Wiper blades that do not clear the screen 5.8%
2007 Mercedes-Benz B-Class 44.4% failed, from 2,234 tests
- Split joint boot 21.0%
- Broken coil spring 13.9%
- Worn steering or suspension joint 12.2%
- Washers that do not work 11.4%
- Brake light out 9.2%
- Corroded brake pipes 8.0%
Shares are of each year's failed tests. Every MOT a particular car has had, with the defects and advisories written at each test, is on GOV.UK's MOT history service from the registration, free.
Mercedes-Benz B-Class problems: common questions
What is the most common problem with a Mercedes-Benz B-Class?
Of the faults that fail an MOT, “Coil spring: fractured or broken” is the most common: it appears on 13.4% of failed Mercedes-Benz B-Class tests. Across categories, lamps, reflectors and electrical equipment is the area that most often fails one, on 35.7% of failed tests.
How often does a Mercedes-Benz B-Class fail its MOT?
27.4% of Mercedes-Benz B-Class tests in 2025 were not passed first time, from 71,047 tests of cars aged three and over. Allowing for the age and mileage of the cars tested, that gives it a UK Motoring Reliability Score of 53 out of 100, where 50 is as expected.
Does anything fail more often on a Mercedes-Benz B-Class than on other cars?
Yes. “Linkage ball joint dust cover no longer prevents the ingress of dirt” appears on 8.9% of its failures against 3.2% for cars of the same age, and “Registration plate lamp(s): inoperative in the case of a single lamp or all lamps” appears on 7.2% of its failures against 3.8% for cars of the same age. Where an item is missing from the national figures for a year, we use the smallest share those figures show, so the comparison never overstates the difference.
Are these the same as breakdowns or known faults?
No. These are the items a tester recorded at the MOT, which covers condition and safety: lamps, brakes, tyres, suspension, corrosion and emissions. A gearbox that is unpleasant, an infotainment screen that has died, or a car that will not start on a cold morning are not part of the test, so they are not in these figures.
Where do the figures come from?
Every normal MOT test of a Mercedes-Benz B-Class aged three and over in Great Britain in 2025, from DVSA's anonymised MOT results. Retests are excluded, and the same fault on more than one wheel counts once.
Data stories to read next
Data sources and methodology
| Figures | Source | Period | Records | Updated |
|---|---|---|---|---|
| MOT defects and advisories | Anonymised MOT tests and results Driver and Vehicle Standards Agency Derived statistics UK Motoring | 2025 | 71,047 MOT tests | 19 September 2026 |
- Shares for defects are of failed tests; shares for advisories are of all tests. A test can carry several defects, so shares add to more than 100%.
- The expected share is what an average car of the same registration years records, weighted by where this model’s failures fall. Where an item is outside the national figures for a year, the smallest share those figures show is used in its place, which is an upper bound, so the comparison never overstates a model’s problems. No expectation is published where less than 80% of the model’s failures can be compared.
- Great Britain only: DVSA does not run MOT testing in Northern Ireland. Cars under three years old are not tested.
- The descriptions of what each part does are general and the same on every model. Every figure comes from the MOT data.
Contains public sector information licensed under the Open Government Licence v3.0.