At a glance
How 11,952 first tests went in 2025.
- Passed first time
- 84 in every 100
- Did not pass first time
- 16 in every 1001,914 failed first-attempt tests
- The typical car
- 8 yearsabout 67,340 miles
- First tests counted
- 11,952
What failed most often
- Suspension arm ball joint (front)25 in every 100 failed tests
- Tyre condition (rear)10 in every 100 failed tests
- Diesel engine warning light9 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 2017 Mercedes-Benz GLC 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
One fault: suspension arm ball joint (front), 6.8 times as often as on similar cars.
Figures below are measured across the 1,908 of 1,914 failed first attempts (99.7%) 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.
Suspension arm ball joint (front)
What it means
A suspension arm ball joint is failed under the general suspension pin, bush or joint wording. Excessively worn is Major, and likely to become detached is graded Dangerous.
Also noted as an advisory
Testers also noted it as an advisory, worn but not yet failing, on 183 first tests, 7.5 times as often as on similar cars.
Data: UK MOT open data, 2025. Compared with cars of the same age and mileage. Advisories count notes recorded on failed first tests only.
Number plates and VIN
Two faults. The strongest is the number plates (front): 4.1 times as often as on similar cars.
Number plates (front)
What it means
A number plate that is missing, illegible, showing an incorrect registration or so insecure that it is likely to fall off is Major. Testers do not measure the characters or their spacing and reject them only if they are obviously incorrect. Delamination and the position of fixing screws or bolts get particular attention, as they can prevent number plate recognition cameras identifying the vehicle.
Number plates (rear)
What it means
A number plate that is missing, illegible, showing an incorrect registration or so insecure that it is likely to fall off is Major. Testers do not measure the characters or their spacing and reject them only if they are obviously incorrect. Delamination and the position of fixing screws or bolts get particular attention, as they can prevent number plate recognition cameras identifying the vehicle.
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, 3.1 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.
Body and structure
One fault: drive shaft joints and boots (front), 2.4 times as often as on similar cars.
Drive shaft joints and boots (front)
Data: UK MOT open data, 2025. Compared with cars of the same age and mileage.
Tyres
One wear pattern: tyre tread depth (rear), 2.1 times as often as on similar cars.
Tyre tread depth (rear)
What it means
Only primary grooves count when tread depth is assessed: those holding the wear indicators, or cut as deep as those when new. Shallower secondary grooves are ignored. Tread depth below the minimum for the vehicle is Dangerous, and so is a pattern not visible over the whole tread, but that second row applies only to vehicles that need the lower minimum.
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
- 84in every 100
- Passed on the first test.
- Fixed at the station
- 2in every 100
- Failed, then fixed at the test station the same day.
- Failed
- 14in every 100
- Did not pass, and were not fixed at the test station.
First-attempt pass 84.0% of 11,952 first tests (2025): only cars that passed first time count. Official-style pass 85.9%: cars fixed at the test station also count as a pass. The 2 fixed and the 14 not fixed make the 16 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, 85 in every 100 passed first time.
| Year | Passed first time | First tests |
|---|---|---|
| 2015 | 83 in every 100 | 1,265 |
| 2016 | 83 in every 100 | 8,746 |
| 2017 This car | 84 in every 100 | 11,952 |
| 2018 | 84 in every 100 | 18,085 |
| 2019 | 86 in every 100 | 16,403 |
| 2020 | 90 in every 100 | 10,628 |
| 2021 | 91 in every 100 | 6,228 |
| 2022 | 91 in every 100 | 6,564 |
If you are buying one
What this year's MOT record means for the decision in front of you.
Mileage matters most on a 2017 Mercedes-Benz GLC.
Of 2017 Mercedes-Benz GLC vehicles with under 49,000 miles, 88 in every 100 passed their 2025 MOT first time. With 88,000 miles or more, 80 in every 100 did.
Petrol or diesel?
| Typical mileage | Passed first time, as tested | Passed first time, same mileage | |
|---|---|---|---|
| Diesel | 67,767 miles | 84 | 84 |
| Petrol | 56,415 miles | 86 | 85 |
Figures are in every 100 first tests. Petrol cars look better on the raw figures only because diesel cars have done more miles (typically 67,767 against 56,415). 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 49,000 | 62,000–73,000 | 88,000 and over | |
|---|---|---|---|
| Suspension arm ball joint (front) | 3.1 | 4.3 | 4.7 |
| Tyre condition (rear) | 1.2 | 1.1 | 1.9 |
| Diesel engine warning light | 1.2 | 1.2 | 1.9 |
| Drive shaft joints and boots (front) | 0.4 | 1.2 | 1.7 |
| Tyre tread depth (front) | 0.6 | 1.1 | 1.6 |
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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