Used car guide · 2004–2022

Smart Forfour common problems and MOT failures

What goes wrong on a used Smart Forfour, year by year: known faults from UK buying guides, the parts flagged at MOT more than on other cars (from 67,129 MOTs done during 2023–2025), and what to check before you buy one.

67,129MOTs done in 2023–2025, all years of this model
25,201on the UK register
2006best year at its MOT

Pick the year

Most years have their own guide. The year is when the car was first registered (it’s on the logbook, or check the reg below).

202220212020201920182017201620152007200620052004

What usually goes wrong with a Smart Forfour?

We haven’t found widely reported faults for the Smart Forfour in the UK buying guides we use yet. That doesn’t mean it has none, so check the car carefully and look at the MOT weak spots below.

Common Smart Forfour MOT failures to check

Parts flagged at MOT well above the usual rate for cars the same age, in more than one year. From the DVSA’s results for every MOT done in Great Britain during 2023–2025.

  • Exhaust emissions (catalyst)

    up to 10.7× usual

    Stands out on cars registered in 2015, 2016 and 2017.

    Rough price £175–£900 (catalytic converter) ClickMechanic

    At the viewing: Look for smoke when revving the warm engine and for engine or DPF warning lights.

  • Brake lights

    up to 2.9× usual

    Stands out on cars registered in 2015, 2016 and 2017.

    Rough price £10–£80 our estimate

    At the viewing: Ask a friend to check every light while you work the switches: indicators, brake lights, fog lights and reversing lights.

  • Ball joint

    up to 2.7× usual

    Stands out on cars registered in 2015, 2016 and 2017.

    Rough price £60–£150 (one joint) ClickMechanic

    At the viewing: Listen for knocking over bumps and check the rubber boots behind the wheels aren't split.

  • Track rod ends

    up to 2.3× usual

    Stands out on cars registered in 2004, 2005 and 2006.

    Rough price £50–£150 (one end, plus about £30–£50 if it needs a wheel alignment) ClickMechanic

    At the viewing: On a straight road the steering wheel should sit straight. Listen for knocks when turning, and check the steering feels even.

  • Ball joint dust cover

    up to 2.2× usual

    Stands out on cars registered in 2004, 2005 and 2006.

    Rough price £60–£150 (one joint) ClickMechanic

    At the viewing: Listen for knocking over bumps and check the rubber boots behind the wheels aren't split.

  • Anti-roll bar link joints

    up to 2.9× usual

    Stands out on cars registered in 2005 and 2015.

    Rough price £60–£150 (one joint) ClickMechanic

    At the viewing: Listen for knocking over bumps and check the rubber boots behind the wheels aren't split.

Smart Forfour MOT pass rate by year

Of the years since 2005 with plenty of MOT tests, the 2006 Smart Forfour did best (57% passed first time, 1 point above all 2006 cars) and the 2015 did worst (68%, 6 points below all 2015 cars). Older cars fail more, so compare each year with all cars registered the same year.

YearPass first timeAll cars that yearMOT tests
201983%85% -25,746
201881%83% -211,318
201777%80% -314,152
201672%77% -515,704
201568%74% -616,282
200746%57% -11168 (small sample)
200657%56% +11,378
200557%57% +01,765
200455%57% -2616

Questions to ask the seller before buying a Smart Forfour

Ask before you travel to see it. A seller who knows the car will have answers, and receipts.

  1. Any recent work on the exhaust emissions (catalyst)? (Flagged at MOT 10.7× as often on the Smart Forfour as on other cars the same age.)
  2. Any recent work on the brake lights? (Flagged at MOT 2.9× as often on the Smart Forfour as on other cars the same age.)
  3. Any recent work on the ball joint? (Flagged at MOT 2.7× as often on the Smart Forfour as on other cars the same age.)
  4. Can I see the service history and receipts for any big jobs?

Looking at a Smart Forfour?

Check the actual car: its own MOT history, whether it already shows these weak spots and what to ask the seller. Free, no sign-up.

Where this comes from: MOT figures are the DVSA’s anonymised results for every MOT test done in Great Britain during 2023–2025, grouped by the year each car was first registered. How many are on the road is from the Department for Transport’s vehicle licensing statistics. Known faults are from UK buying guides, in our own words, with links. How we score