Smart (mcc) Forfour common problems

By component

What wears out on a Forfour

Failure items grouped by the part behind them, with the share of failed Smart (mcc) Forfour tests recording each. A part can carry several DVSA wordings; they are listed beneath. One failed test often lists several items, so shares do not sum to 100%.

1. 1.Tyres

   40.8% of failed tests

   Tread wears with every mile and sidewalls age and take kerb damage; the legal minimum is 1.6 mm across the central three-quarters.

   • “Tyre tread depth not in accordance with the requirements” — explained19.2%
   • “A tyre cords visible or damaged” — explained8.1%
   • “A tyre seriously damaged” — explained6.8%
   • “A tyre seriously damaged” — explained3.5%

   Across all cars, tyres failures run at a similar rate at every age, because they are replaced on a cycle rather than wearing out with the car. How long tyres last

2. 2.Suspension bushes

   26.6% of failed tests

   Rubber bushes in arms and links perish and split with age and load; the most recorded suspension item on the test.

   • “A suspension pin, bush or joint excessively worn” — explained15.8%
   • “A suspension pin, bush or joint excessively worn” — explained4.3%
   • “A suspension pin, bush or joint excessively worn” — explained2.9%
   • “A suspension joint dust cover missing or no longer prevents the ingress of dirt etc” — explained2.4%

   Across all cars, suspension bushes failures climb 20-fold between three and fifteen years, peaking at 15+ years. How long suspension bushes last

3. 3.Catalytic converter and emissions

   17.6% of failed tests

   Catalysts degrade with age and misfires; a failed emissions reading is usually the catalyst, a lambda sensor or a tired engine.

   • “Lambda coefficient outside the default limits or the range specified by the manufacturer” — explained13.8%
   • “Emissions levels exceed the manufacturer's specified limits” — explained2.6%
   • “Emissions levels exceed default limits” — explained1.3%

4. 4.Wiper blades and washers

   17.4% of failed tests

   Rubber blades harden and split within a year or two; washer jets block and pumps fail.

   • “Wiper blade missing or obviously not clearing the windscreen” — explained11.2%
   • “Windscreen washers not working or not providing sufficient fluid to clear the windscreen” — explained3.8%
   • “Windscreen washers not working or not providing sufficient fluid to clear the windscreen” — explained2.3%

   Across all cars, wiper blades and washers failures run at a similar rate at every age, because they are replaced on a cycle rather than wearing out with the car. How long wiper blades and washers last

5. 5.Bulbs and lamps

   16.6% of failed tests

   Filament bulbs simply expire; the cheapest and most avoidable failure on the test, and one of the most recorded.

   • “Stop lamp missing, inoperative or in the case of a multiple light source more than 1/2 not functioning” — explained8.9%
   • “A rear registration plate lamp or light source missing or inoperative in the case of a single lamp or all lamps” — explained3.1%
   • “A lamp missing, inoperative or in the case of a multiple light source more than 1/2 not functioning” — explained2.0%
   • “Lamp emitted colour, position or intensity not in accordance with the requirements” — explained1.5%

   Across all cars, bulbs and lamps failures climb 15-fold between three and fifteen years, peaking at 15+ years. How long bulbs and lamps last

6. 6.Coil springs

   9.8% of failed tests

   Springs fatigue and corrode where the coating chips, then snap, often at the bottom coil; potholes and salt accelerate it.

   • “A spring or spring component fractured or seriously weakened” — explained9.8%

   Across all cars, coil springs failures climb 20-fold between three and fifteen years, peaking at 12–14 years. How long coil springs last

7. 7.Exhaust system

   8.8% of failed tests

   Silencers and pipes rust through from the inside on short-trip cars; rubber hangers perish.

   • “Exhaust system leaking or insecure” — explained7.1%
   • “An induction or exhaust leak that could affect emissions levels” — explained1.7%

   Across all cars, exhaust system failures climb 104-fold between three and fifteen years, peaking at 15+ years. How long exhaust system last

8. 8.Brake discs

   7.4% of failed tests

   Discs thin with each pad set and pit or corrode when lightly used; failure is for significant wear, fracture or insecurity, advisory for surface condition.

   • “Brake disc or drum significantly and obviously worn” — explained4.9%
   • “Brake disc or drum excessively weakened, insecure or fractured” — explained1.5%
   • “Excessive fluctuation in brake effort through each wheel revolution.” — explained1.1%

   Across all cars, brake discs failures climb 3-fold between three and fifteen years, peaking at 12–14 years. How long brake discs last

By registration year

Forfour problems by year

MOT pass rate for Smart (mcc) Forfour cars by the year they were first registered, from years with at least 1,000 tests. Every car in a row is the same age, so the rate is raw. Neighbouring years differ by a year of wear — a step of a point or two is age. The step at 2017, up 5.1 points, is larger than wear explains and most likely marks a change in the cars themselves.

Last column: change on the previous year, in points. Years registered within the last three years have not yet been tested and are not shown.

Before it fails

What testers warn Forfour owners about

Advisories are the same parts a year or two earlier. Share of all Smart (mcc) Forfour tests carrying an advisory for each.

• Tyres47.7% of tests
• Brake discs19.9% of tests
• Suspension bushes7.3% of tests
• Brake pads and shoes6.3% of tests
• Bulbs and lamps2.2% of tests

Go deeper

The rest of the Forfour file

• Smart (mcc) Forfour: pass rate, ranking and the full failure record
• Is a Forfour's mileage high for its age?
• Every Smart (mcc) model compared
• Check a specific car's MOT history

Common questions

What are the most common problems with a Smart (mcc) Forfour?

Going by what fails the MOT, tyres (recorded in 40.8% of failed tests), suspension bushes (recorded in 26.6% of failed tests), and catalytic converter and emissions (recorded in 17.6% of failed tests). These are the items testers actually record across 22,245 tests, not reports from owners, so they describe what goes wrong at the point where it has to be fixed.

Which Smart (mcc) Forfour year is the most reliable?

By MOT pass rate, Smart (mcc) Forfour cars registered in 2019 do best at 80.9% and 2015 cars do worst at 66.1%. Most of that ordering is simply age — newer cars pass more — so read the year table for steps larger than a couple of points between neighbouring years; those mark a change in the cars rather than the calendar. The largest such step is at 2017, up 5.1 points on 2016.

Is the Smart (mcc) Forfour reliable?

Adjusted for the age and mileage of the cars tested, the Smart (mcc) Forfour passes 64.8% of MOTs against a national 72.3%. An MOT measures roadworthiness on the day rather than breakdowns or running costs, so this is a reliability measure in the narrow sense: how often the car meets the legal standard, and what stops it.

What should I check when buying a used Smart (mcc) Forfour?

Start with what fails most: tyres, suspension bushes, wiper blades and washers. Then read the car's own MOT history for advisories carried year to year without repair — the model tells you what to expect, the history tells you whether this owner dealt with it.