Model Reports 5 min read Updated 18 Oct 2026

Smart (MCC) Forfour 2015: reliability & common MOT faults

In 2025, 66 in every 100 first MOTs on a 2015 Smart (MCC) Forfour were passes. Most common reason for a fail: Suspension arm ball joint (front).

Summary

A 2015 Smart (MCC) Forfour passed first time about 5 in every 100 less often than the 2016 model year next to it.

At a glance

How 5,198 first tests went in 2025.

Passed first time
66 in every 100
Did not pass first time
34 in every 1001,776 failed first-attempt tests
The typical car
10 yearsabout 52,821 miles
First tests counted
5,198

What failed most often

  1. Suspension arm ball joint (front)16 in every 100 failed tests
  2. Petrol emissions (with catalyst)15 in every 100 failed tests
  3. Coil spring (front)10 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.

Note:

These are patterns across 2015 Smart (MCC) Forfour 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.

Noise, emissions and leaks

Two faults. The strongest is the petrol emissions (with catalyst): 6.1 times as often as on similar cars.

Figures below are measured across the 1,775 of 1,776 failed first attempts (99.9%) 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.

Petrol emissions (with catalyst)

Failed on 259 first tests6.1 times as often as similar carsStrong evidence

What it means

Emissions levels over the manufacturer's specified limits are Major, as are levels over default limits, which apply when no exact match is found for the vehicle. Dense blue or clearly visible black smoke at idle, held for a set period, is Major, except for certain older vehicles and two stroke engines where smoke is unavoidable. An induction or exhaust leak that could affect emissions levels is Major too.

Petrol emissions not tested

Failed on 58 first tests4.9 times as often as similar carsLikely evidence

What it means

On a petrol car, an emissions test recorded as not tested or unable to be completed is failed as Major. DVSA's wording gives no reason why.

Data: UK MOT open data, 2025. Compared with cars of the same age and mileage.

Tyres

One wear pattern: tyre tread depth (rear), 3.9 times as often as on similar cars.

Tyre tread depth (rear)

Failed on 143 first tests3.9 times as often as similar carsWear pattern

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.

Also noted as an advisory

Testers also noted it as an advisory, worn but not yet failing, on 269 first tests, 2.1 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.

Suspension

Two faults. The strongest is the anti-roll bar linkage ball joints (front): 3.5 times as often as on similar cars.

Anti-roll bar linkage ball joints (front)

Failed on 77 first tests3.5 times as often as similar carsLikely evidence

What it means

Excessive wear on an anti-roll bar linkage ball joint is Major. A joint 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 55 first tests, 4.1 times as often as on similar cars.

Suspension arm ball joint (front)

Failed on 283 first tests3.1 times as often as similar carsLikely evidence

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 55 first tests, 2.1 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.

Body and structure

One fault: exhaust system (rear), 3.4 times as often as on similar cars.

Exhaust system (rear)

Failed on 73 first tests3.4 times as often as similar carsLikely evidence

What it means

Exhaust fumes causing a danger to health of persons on board are graded Dangerous, and so is a silencer likely to become detached. Fumes entering the cabin are Major. One or more missing or defective mountings does not necessarily make the exhaust insecure, since testers assess the overall security of the system.

Data: UK MOT open data, 2025. Compared with cars of the same age and mileage.

Lamps and electrical

One fault: brake light (rear), 2.9 times as often as on similar cars.

Brake light (rear)

Failed on 166 first tests2.9 times as often as similar carsPossible evidence

What it means

All stop lamps missing or not working is graded Dangerous, and so is a stop lamp that stays on when the brakes are released. A stop lamp that is missing or not working is Major. On some vehicles with LED rear lamps, part of the stop lamp can go out when the rear fog lamp is lit, which is not regarded as a defect.

Data: UK MOT open data, 2025. Compared with cars of the same age and mileage.

Advisories

Other things testers noted as worn or close to failing, more often than on similar cars.

An advisory is a note from the tester about something that has not failed yet. It is an early warning, not a fail. Advisories for the faults above are shown with those faults.

Macpherson strut (front)

Noted on 23 first tests3.7 times as often as similar carsElevated evidence

Individual direction indicators (rear)

Noted on 34 first tests3.3 times as often as similar carsElevated evidence

Data: UK MOT open data, 2025. Counts cover advisories recorded on failed first tests only, 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
66in every 100
Passed on the first test.
Fixed at the station
6in every 100
Failed, then fixed at the test station the same day.
Failed
28in every 100
Did not pass, and were not fixed at the test station.

First-attempt pass 65.8% of 5,198 first tests (2025): only cars that passed first time count. Official-style pass 72.3%: cars fixed at the test station also count as a pass. The 6 fixed and the 28 not fixed make the 34 in every 100 that did not pass first time.

Same model, other years

Passed first time in every 100, all tested in 2025.

40608010020152016201720182019202020212022Newer cars
40608010020152020Newer cars

Newer cars are younger, so look for a jump rather than the climb. A year earlier (2024), when these cars were a year younger, 67 in every 100 passed first time.

YearPassed first timeFirst tests
2015 This car66 in every 1005,198
201670 in every 1005,053
201776 in every 1004,586
201880 in every 1003,687
201981 in every 1001,880
202084 in every 100600
202183 in every 100583
202289 in every 100565

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 Forfour.

Of 2015 Forfour vehicles with under 37,000 miles, 76 in every 100 passed their 2025 MOT first time. With 73,000 miles or more, 58 in every 100 did.

Under 37,0001,019 tests
76
37,000–48,0001,078 tests
70
48,000–58,000 Typical car985 tests
64
58,000–73,0001,100 tests
61
73,000 and over1,015 tests
58

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 37,00048,000–58,00073,000 and over
Suspension arm ball joint (front)2.35.36.9
Petrol emissions (with catalyst)2.15.07.7
Coil spring (front)2.63.24.7
Brake light1.82.93.9
Tyre tread depth (rear)0.92.95.1

Faults per 100 first tests, by the car's mileage at the test.

When a car fails

42in every 100

of failed cars had one item to fix.

28in every 100

of failed cars had three or more items to fix.

8in every 100

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.

A 2015 Smart (MCC) Forfour passed first time about 5 in every 100 less often than the 2016 model year next to it. In 2025, 65.8% of 5,198 first MOTs on the 2015 Smart (MCC) Forfour passed first time (PRS: items fixed at the station the same day, counted as a fail). The official-style rate including PRS is 72.3%. Among 1,776 failed first-attempt MOT tests (test year 2025), Petrol emissions (with catalyst) appears more often than on similar cars (14.6% of those tests; 259 observed failures; about 6.1× more often than similar cars). There is no single reliability score here; this is a pre-purchase checklist built from DVSA open data, not a guarantee for any individual car.
Ranked by how often they were actually recorded, the items that most often failed a 2015 Smart (MCC) Forfour at the first attempt were Suspension arm ball joint (front) (15.9%), Petrol emissions (with catalyst) (14.6%) and Coil spring (front) (10.3%), each as a share of the year's failed first attempts. That is what goes wrong most often on the car. The common faults table shows a different measure: faults that are unusual compared with similar cars.
Among failed first-attempt tests we highlight patterns that appear more often than on similar cars. Top example: Petrol emissions (with catalyst) (14.6% of those tests; 259 observed failures; about 6.1× more often than similar cars). These are statistical signals, not a diagnosis of any individual car.
Petrol emissions (with catalyst) shows up more often than on similar cars (14.6% of those tests; 259 observed failures; about 6.1× more often than similar cars). That does not prove a design fault. Age, mileage, and how the car was used still matter. Treat it as a pre-purchase checkpoint, not a manufacturer service bulletin.
Common MOT problem areas for the 2015 Smart (MCC) Forfour include Petrol emissions (with catalyst), Petrol emissions not tested, Anti-roll bar linkage ball joints (front). These are the faults that stand out compared with similar cars, not a complete list of what can go wrong on any individual car.
Advisories flag issues noted at the test and are not a fail rate. We show advisory patterns that appear more often than on similar cars among failed first-attempt tests, separate from common failure rows. Use them as early-warning checks, not as a pass/fail score.
This page highlights MOT failure patterns for the 2015 Smart (MCC) Forfour (registration year) using UK DVSA open data for the selected test year. Patterns are compared with cars of a similar age and mileage. It is a buyer checklist from MOT defect statistics, not a full service history or manufacturer service-bulletin list.
No. MOT tests do not cover engine internals, gearboxes, or many electronic modules. Patterns here come from MOT defect statistics only and should not be read as engine or gearbox reliability scores.

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.

2024 2025

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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