2025 MOT results
Smart Forfour common problems
The most common reason a Smart Forfour fails its MOT is a brake light out, on 11.4% of its 6,575 failed tests in 2025. Against other cars of the same age, 5 faults stand out, the widest gaps being: emissions above the limit at 10.6% of failures against 1.7% expected; an exhaust leak at 5.6% of failures against 1.8% expected; a worn steering or suspension joint at 10.8% of failures against 4.6% expected.
- Tests in 2025 23,220 Cars aged three and over
- Failed first time 28.3% 6,575 tests
- Found a dangerous defect 7.5% Unsafe to drive away
- Ended with an advisory 48.4% A problem to watch, not a failure
What fails a Smart Forfour MOT
Each bar is the share of failed Smart Forfour 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 |
|---|---|
| Stop lamp: not working Lamps, reflectors and electrical equipment | 11.4% |
| Tyres: tread depth below requirements of 1.6mm Tyres | 11.3% |
| Suspension arms: ball joint excessively worn Suspension | 10.8% |
| Catalyst emissions: lambda reading after 2nd fast idle outside specified limits Noise, emissions and leaks | 10.6% |
| Wipers: does not clear the windscreen effectively Visibility | 10.2% |
| Coil spring: fractured or broken Suspension | 7.3% |
| Washers: provides insufficient washer liquid Visibility | 6.7% |
| Malfunction indicator lamp: inoperative or indicates a malfunction Noise, emissions and leaks | 6.4% |
| Tyres: ply or cords exposed Tyres | 5.7% |
| Exhaust system: major leak of exhaust gases Body, chassis, structure | 5.6% |
| Brake pads: less than 1.5 mm thick Brakes | 5.5% |
| Tyres: cut in excess of the requirements deep enough to reach the ply or cords Tyres | 4.5% |
Source:DVSA,UK Motoring analysis 2025 Updated
-
Brake light out
11.4% of failures 4.9% expected 2.3 times as often
A brake light not working, from a bulb, a poor earth, or the switch on the pedal.
Reverse up to a wall or window at dusk and press the pedal to see all three lamps light.
-
Tyre worn below the legal limit
11.3% of failures 9.0% expected somewhat more often
A tyre worn past the 1.6mm legal minimum across the middle three quarters of the tread.
A 20p coin in the main grooves: if the outer band of the coin is visible, the tyre is close to the limit.
-
Worn steering or suspension joint
10.8% of failures 4.6% expected 2.3 times as often
Play in a steering or suspension joint, where a worn ball and socket lets the wheel move where it should not.
A knock at low speed over rough ground, or vague steering, is the usual warning.
-
Emissions above the limit
10.6% of failures 1.7% expected 6.2 times as often
The exhaust gases are outside the limits for the car, which can be the catalytic converter, a sensor, or simply a poor state of tune.
A long run before the test helps a catalyst get hot; a persistent failure usually needs a diagnosis.
-
Wiper blades that do not clear the screen
10.2% of failures 6.7% expected 1.5 times as often
Wiper blades that leave the windscreen smeared or streaked across the area the driver looks through.
Look for split or hardened rubber, and lift each blade to see whether it still sits flat.
-
Broken coil spring
7.3% of failures 8.7% expected somewhat less 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.
Which parts of the car fail
Lamps, reflectors and electrical equipment is the area that most often fails a Smart Forfour, on 30.0% of failed tests. The widest gap against cars of the same registration years is noise, emissions and leaks, on 20.5% against 10.2% 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 | 30.0% |
| Tyres | 27.2% |
| Suspension | 27.2% |
| Noise, emissions and leaks | 20.5% |
| Visibility | 20.3% |
| Brakes | 13.5% |
| Body, chassis, structure | 9.7% |
| Steering | 3.1% |
Source:DVSA,UK Motoring analysis 2025 Updated
What testers warn about
48.4% of Smart Forfour tests ended with at least one advisory: a fault the tester found that did not fail the test. On Smart Forfours, 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 | 19.3% |
| Brake discs: worn, pitted or scored, but not seriously weakened Brakes | 11.4% |
| Tyres: slightly damaged or cracking or perishing Tyres | 10.0% |
| Brake pads: wearing thin Brakes | 5.7% |
| Brake discs: worn, but not excessively Brakes | 4.0% |
| Suspension arms: pin or bush worn but not resulting in excessive movement Suspension | 2.8% |
| Engine oil leak, but not excessive Noise, emissions and leaks | 2.6% |
| Exhaust system: minor leak of exhaust gases Body, chassis, structure | 2.1% |
| Registration plates: deteriorated but not likely to be misread Identification of the vehicle | 1.9% |
| Coil spring: corroded Suspension | 1.7% |
| Child seat fitted not allowing full inspection of adult belt Non-component advisories | 1.6% |
| Suspension arms: ball joint has slight play Suspension | 1.5% |
Source:DVSA,UK Motoring analysis 2025 Updated
Smart Forfour problems: common questions
What is the most common problem with a Smart Forfour?
Of the faults that fail an MOT, “Stop lamp: not working” is the most common: it appears on 11.4% of failed Smart Forfour tests. Across categories, lamps, reflectors and electrical equipment is the area that most often fails one, on 30.0% of failed tests.
How often does a Smart Forfour fail its MOT?
28.3% of Smart Forfour tests in 2025 were not passed first time, from 23,220 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 36 out of 100, where 50 is as expected.
Does anything fail more often on a Smart Forfour than on other cars?
Yes. “Catalyst emissions: lambda reading after 2nd fast idle outside specified limits” appears on 10.6% of its failures against 1.7% for cars of the same age, and “Exhaust system: major leak of exhaust gases” appears on 5.6% of its failures against 1.8% 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 Smart Forfour 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 | 23,220 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.