At a glance
How 5,481 first tests went in 2025.
- Passed first time
- 76 in every 100
- Did not pass first time
- 24 in every 1001,290 failed first-attempt tests
- The typical car
- 10 yearsabout 65,922 miles
- First tests counted
- 5,481
What failed most often
- Tyre condition (front)15 in every 100 failed tests
- Coil spring (rear)15 in every 100 failed tests
- Anti-roll bar linkage ball joint dust cover (front)12 in every 100 failed tests
How we count this. Data: UK MOT open data, 2025. Only Class 4 cars on their first MOT of the year are counted. A car that fails and is fixed at the test station still counts as a fail in the first-attempt rate. These are raw results, not adjusted for age, mileage, or peer mix. The MOT does not test engine or gearbox internals.
These are patterns across 2015 Mercedes-Benz B-Class vehicles in 2025, not a prediction that any one car will have them. Faults are grouped by part of the car. A wear pattern follows age and use more than the way the car was built. They come from MOT defect codes, not manufacturer bulletins, recalls or a diagnosis of any one car.
Suspension
Three faults. The strongest is the anti-roll bar linkage ball joint dust cover (front): 7.0 times as often as on similar cars.
Figures below are measured across the 1,287 of 1,290 failed first attempts (99.8%) that recorded an odometer reading in 2025. Mileage is needed to compare like with like.
We only list faults with at least 20 failures and a rate of about 2.0 times that of similar cars, which keeps one-off results out of the list.
Anti-roll bar linkage ball joint dust cover (front)
What it means
A suspension joint dust cover that is severely deteriorated is Minor. It becomes Major once it is missing or no longer prevents the ingress of dirt, so what matters is whether it still keeps dirt out. DVSA words this for any suspension joint dust cover, and files it here under anti-roll bars.
Anti-roll bar ball joint dust cover (front)
Coil spring (rear)
What it means
A missing bump stop rubber is not a reason to fail a coil spring. When the vehicle is jacked and lowered, a spring that does not correctly locate as the suspension returns to its normal running position is rejected as insecurely attached. A missing spring is Major, and graded Dangerous where directional control is affected.
Data: UK MOT open data, 2025. Compared with cars of the same age and mileage.
Seat belts and restraints
One fault: airbag warning light, 4.8 times as often as on similar cars.
Airbag warning light
What it means
The airbag warning lamp (SRS MIL in DVSA's wording) is failed only if it indicates a system malfunction, which is Major. A lamp lit to show the passenger airbag is disabled is not to be regarded as a defect. Dashboard messages are not a defect in their own right, though they can help the tester confirm a malfunction.
Data: UK MOT open data, 2025. Compared with cars of the same age and mileage.
Lamps and electrical
One fault: number plate lights (rear), 4.6 times as often as on similar cars.
Number plate lights (rear)
What it means
Registration plate lamps must light up the rear registration plate and operate at the same time as the position lamps. A missing or inoperative lamp is Major when the plate has only one lamp or all its lamps are not working, and Minor when the plate has several lamps or light sources and not all have failed. A lamp throwing direct white light to the rear is also Minor.
Data: UK MOT open data, 2025. Compared with cars of the same age and mileage.
Noise, emissions and leaks
One fault: diesel engine warning light, 2.5 times as often as on similar cars.
Diesel engine warning light
What it means
An engine malfunction indicator lamp that is illuminated to show a malfunction is graded Major on a diesel, but only on the diesels the test covers, which depends on the vehicle type and when it was first used. DVSA lists it under exhaust emissions for compression ignition engines, and the detail line for the row also names an inoperative lamp.
Data: UK MOT open data, 2025. Compared with cars of the same age and mileage.
Tyres
One wear pattern: tyre condition (front), 2.0 times as often as on similar cars.
Tyre condition (front)
What it means
Exposed or damaged ply or cords are graded Dangerous. A cut in excess of the requirements and deep enough to reach the ply or cords is Major, and testers may open the cut with a blunt instrument to check its depth. A tyre contacting the vehicle through flexing or suspension movement is not a defect; fouling fails only at the time of test.
Data: UK MOT open data, 2025. Compared with cars of the same age and mileage.
MOT pass rates
How first tests ended, and how the pass rates are counted.
- Passed first time
- 76in every 100
- Passed on the first test.
- Fixed at the station
- 5in every 100
- Failed, then fixed at the test station the same day.
- Failed
- 19in every 100
- Did not pass, and were not fixed at the test station.
First-attempt pass 76.5% of 5,481 first tests (2025): only cars that passed first time count. Official-style pass 80.6%: cars fixed at the test station also count as a pass. The 5 fixed and the 19 not fixed make the 24 in every 100 that did not pass first time.
Petrol and diesel
Figures are in every 100 first tests. Cars with more miles usually fail more often, so the same-mileage figure gives every fuel the mileage mix of all the cars in this year.
Same model, other years
Passed first time in every 100, all tested in 2025.
Newer cars are younger, so look for a jump rather than the climb. A year earlier (2024), when these cars were a year younger, 78 in every 100 passed first time.
| Year | Passed first time | First tests |
|---|---|---|
| 2005 | 53 in every 100 | 309 |
| 2006 | 56 in every 100 | 1,552 |
| 2007 | 55 in every 100 | 2,116 |
| 2008 | 55 in every 100 | 2,936 |
| 2009 | 58 in every 100 | 3,849 |
| 2010 | 58 in every 100 | 4,152 |
| 2011 | 58 in every 100 | 3,257 |
| 2012 | 69 in every 100 | 5,571 |
| 2013 | 71 in every 100 | 6,793 |
| 2014 | 71 in every 100 | 7,934 |
| 2015 This car | 76 in every 100 | 5,481 |
| 2016 | 79 in every 100 | 5,183 |
| 2017 | 80 in every 100 | 5,502 |
| 2018 | 83 in every 100 | 3,858 |
| 2019 | 89 in every 100 | 4,149 |
| 2020 | 90 in every 100 | 2,786 |
| 2021 | 92 in every 100 | 1,727 |
| 2022 | 91 in every 100 | 1,216 |
If you are buying one
What this year's MOT record means for the decision in front of you.
Mileage matters most on a 2015 B-Class.
Of 2015 B-Class vehicles with under 44,000 miles, 86 in every 100 passed their 2025 MOT first time. With 91,000 miles or more, 69 in every 100 did.
Petrol or diesel?
| Typical mileage | Passed first time, as tested | Passed first time, same mileage | |
|---|---|---|---|
| Diesel | 69,105 miles | 75 | 76 |
| Petrol | 47,628 miles | 83 | 80 |
Figures are in every 100 first tests. Petrol cars look better on the raw figures only because diesel cars have done more miles (typically 69,105 against 47,628). At the same mileage there is no clear difference between the two.
What to check at your mileage
How often each fault turned up on a failed first test, by the car's mileage. Read it as: what is likely to need looking at on a car like the one in front of you.
| Under 44,000 | 59,000–73,000 | 91,000 and over | |
|---|---|---|---|
| Tyre condition (front) | 2.4 | 3.2 | 4.7 |
| Coil spring (rear) | 2.5 | 3.3 | 5.2 |
| Anti-roll bar linkage ball joint dust cover (front) | 1.1 | 2.9 | 4.5 |
| Number plate lights | 0.6 | 2.7 | 3.5 |
| Diesel engine warning light | 0.6 | 0.8 | 2.0 |
Faults per 100 first tests, by the car's mileage at the test.
When a car fails
of failed cars had one item to fix.
of failed cars had three or more items to fix.
of all first tests had a defect the tester marked dangerous (unsafe to drive away).
Every figure here is a first-attempt MOT rate from DVSA open data for this model line, for cars of this model year tested in 2025. Each mileage band holds a fifth of the tests. MOTs do not test engine or gearbox internals, so this is a pre-purchase checklist, not a full reliability score.
FAQs
Short answers about how to read this model-year guide.
About this data
How this page is built and what it can (and can't) say.
These figures come from UK MOT open data for this model year. We surface common failure patterns against similar cars, not a full reliability score, and not a pass/fail verdict on any individual vehicle.
What we include
UK Class 4 cars only. Normal MOT tests (not retests); first test per vehicle per calendar year; results pass, PRS, or fail.
Same-day repairs
PRS means the car failed items that were fixed at the test station and then passed the same day. We count PRS as a first-attempt fail in headline rates so same-day repairs do not hide problems.
How we compare
We compare this model year with other Class 4 cars of similar age and mileage in the same test year. This model family is left out of the peer group so the car is not measured against itself.
What this does not cover
- MOTs do not cover engine internals, gearboxes, or many electronics; this is not a full reliability score.
- Common faults come from MOT defect stats, not manufacturer TSBs or recalls.
- Age and mileage matching reduces, but does not remove, differences in how cars were used and maintained.
- If the data for a car is too thin to say anything useful, we say so rather than guess.
Contains public sector information licensed under the Open Government Licence v3.0.
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