Common problems
Smart Forfour common problems
What MOT testers find on the Smart Forfour: the parts that fail or get advisories most often at each age, against all cars of the same age. From 89,645 DVSA MOT tests taken 2022 to 2025. These figures cover cars first used 2014 or later. Earlier cars sold under the same name are not included; see Smart Forfour cars first used before 2014.
MOT data updated
At 7 years, the most tested age
What stands out
- Windscreen, wipers and mirrors fails show up on 5.7 of every 100 MOTs of a Smart Forfour at 7 years old (n=19,511), against 3.4 for all cars of that age (n=10,537,318).
- Brakes fails are less common: 3.1 per 100 MOTs against 4.1 for all cars at the same age.
- The fail item testers record most often at 7 years: tyre tread below 1.6 mm, on 3.4 per 100 MOTs (all cars 2.2).
- The most common advisory or minor defect: tread depth: worn close to legal limit/worn on edge, on 17.5 per 100 MOTs.
Problems by part at 7 years
How many of every 100 MOTs found a fail, or an advisory or minor defect, in each area. A test with faults in two areas counts in both.
| Area | Fails | All cars | Advisories | All cars |
|---|---|---|---|---|
| Tyres | 8.1 | 6.0 | 27.3 | 24.8 |
| Lights and electrics | 5.8 | 5.8 | 1.9 | 2.5 |
| Windscreen, wipers and mirrors | 5.7 | 3.4 | 3.1 | 3.3 |
| Suspension | 4.7 | 4.4 | 5.1 | 8.7 |
| Exhaust, emissions and leaks | 3.6 | 1.7 | 1.3 | 1.7 |
| Brakes | 3.1 | 4.1 | 17.4 | 17.9 |
| Body and structure | 1.4 | 1.3 | 1.2 | 1.6 |
| Number plates and VIN | 0.2 | 0.2 | 1.1 | 1.2 |
| Seat belts and airbags | 0.2 | 0.4 | 0.2 | 0.3 |
| Steering | 0.2 | 0.8 | 0.3 | 1.1 |
| Road wheels | 0.1 | 0.3 | 0.7 | 0.6 |
What testers fail most on the Forfour at 7 years
| Item | Area | Per 100 MOTs | All cars | Typical repair (estimate) |
|---|---|---|---|---|
| Tyre tread below 1.6 mm | Tyres | 3.4 | 2.2 | £88 to £145 per tyre |
| Wipers not clearing screen | Windscreen, wipers and mirrors | 3.3 | 1.7 | £15 to £30 per blade |
| Brake light not working | Lights and electrics | 2.6 | 0.9 | £10 to £47 per lamp |
| Suspension ball joint worn | Suspension | 2.3 | 0.7 | £75 to £237 per side (rough guide) |
| Catalyst emissions: Lambda reading after 2nd fast idle outside specified limits | Exhaust, emissions and leaks | 2.0 | 0.2 | |
| Washers: provides insufficient washer liquid | Windscreen, wipers and mirrors | 1.9 | 1.0 | £2 to £14 per car (rough guide) |
| Tyre with cords exposed | Tyres | 1.8 | 1.1 | £88 to £145 per tyre |
| Brake pads under 1.5 mm | Brakes | 1.8 | 2.0 | £72 to £174 per axle (rough guide) |
| Tyre condition: has a cut in excess of the requirements deep enough to reach the ply or cords | Tyres | 1.3 | 1.3 | £88 to £145 per tyre |
| Malfunction indicator lamp: inoperative or indicates a malfunction | Exhaust, emissions and leaks | 1.2 | 0.6 | diagnosis from £39 (rough guide) |
Early warnings: advisories and minor defects at 7 years
Advisories and minor defects are recorded, but the car still passes. Across all cars, a part with an advisory or minor defect failed at the next MOT 5.5 times in 100 (n=88,666,940 pairs of consecutive MOTs), against 0.3 times in 100 when the same part had none (n=12,936,860,350).
| Item | Area | Per 100 MOTs | All cars | If it needs replacing (estimate) |
|---|---|---|---|---|
| Tread depth: worn close to legal limit/worn on edge | Tyres | 17.5 | 15.0 | £88 to £145 per tyre |
| Brake discs: worn, pitted or scored, but not seriously weakened | Brakes | 9.9 | 8.0 | £148 to £376 per axle (rough guide) |
| Tyre condition: slightly damaged/cracking or perishing | Tyres | 9.5 | 8.9 | £88 to £145 per tyre |
| Brake pads: wearing thin | Brakes | 6.0 | 9.0 | £72 to £174 per axle (rough guide) |
| Brake discs: worn, but not excessively | Brakes | 4.2 | 2.6 | £148 to £376 per axle (rough guide) |
| Tread depth: worn close to legal limit/worn on edge | Tyres | 2.4 | 2.0 | £88 to £145 per tyre |
| Child Seat fitted not allowing full inspection of adult belt | Other | 1.7 | 2.4 | |
| Suspension arm pins and bushes: pin or bush worn but not resulting in excessive movement | Suspension | 1.5 | 3.0 | £92 to £237 per arm (rough guide) |
| Wipers: blade defective | Windscreen, wipers and mirrors | 1.4 | 1.0 | |
| Windscreen: damaged but not adversely affecting driver's view | Windscreen, wipers and mirrors | 1.3 | 1.9 |
Repair estimates are a guide for an independent garage: labour at the national median local garage rate (median £78 an hour from 65 garages, ONS price quotes) times estimated labour hours, plus a parts band. Labour hours and most parts bands are estimates, not quotes, and prices vary by model, engine and region. A warning light fault shows the cost of the diagnosis only.
How problems change with age
| Age | Tests (n) | Tyres | Lights and electrics | Windscreen, wipers and mirrors |
|---|---|---|---|---|
| 3 years | 3,863 | 4.8 | 2.1 | 4.3 |
| 4 years | 7,076 | 5.3 | 2.2 | 8.7 |
| 5 years | 11,275 | 7.0 | 3.2 | 6.2 |
| 6 years | 15,976 | 7.5 | 4.2 | 5.9 |
| 7 years | 19,511 | 8.1 | 5.8 | 5.7 |
| 8 years | 15,678 | 8.2 | 6.8 | 5.9 |
| 9 years | 10,821 | 8.2 | 8.4 | 6.1 |
| 10 years | 5,445 | 8.4 | 9.9 | 6.0 |
Mileage
At 7 years, Smart Forfour cars showing under 30,000 miles failed 16.2% of MOTs (n=6,582); the band that failed most, 60,000 to 90,000 miles, failed 33.9% (n=2,080). For pass and fail rates by age, see Smart Forfour MOT fail rates.
What to check on a viewing
On the Smart Forfour, testers most often record tyre tread below 1.6 mm; wipers not clearing screen; brake light not working. Look at these first, then the areas below.
Tyres
- Check the tread across the full width of all four tyres, and the spare if there is one.
- Look for cuts, bulges and cracking in the sidewalls.
- Wear on one edge only can point to worn suspension or the tracking being out.
Lights and electrics
- With someone outside, try every light: dipped and main beam, indicators, brake lights, fog lights and number plate lamps.
- Check that the warning lights come on with the ignition and go out once the engine runs.
- Look for misted, cracked or yellowed headlamp lenses.
Windscreen, wipers and mirrors
- Look for chips or cracks in the windscreen, above all in front of the driver.
- Run the wipers and washers: they should clear the screen without smearing.
- Check that the mirrors are present, secure and not cracked.
Ask for the car's MOT history and service record: advisories that repeat from one year to the next show what has been left. GOV.UK MOT history.
Questions
What are the most common problems on the Smart Forfour?
At 7 years, the age with the most MOT tests (19,511), the fail items testers record most often on the Smart Forfour are tyre tread below 1.6 mm (3.4 per 100 MOTs), wipers not clearing screen (3.3 per 100 MOTs), brake light not working (2.6 per 100 MOTs). The most common advisories or minor defects are tread depth: worn close to legal limit/worn on edge (17.5) and brake discs: worn, pitted or scored, but not seriously weakened (9.9).
Which parts of the Smart Forfour fail more often than on other cars?
At 7 years: windscreen, wipers and mirrors (5.7 per 100 MOTs against 3.4 for all cars); tyres (8.1 per 100 MOTs against 6.0 for all cars); exhaust, emissions and leaks (3.6 per 100 MOTs against 1.7 for all cars). Compared with 10,537,318 MOTs of all cars the same age.
Smart Forfour problems by area
More on the Smart Forfour
Other Smart models
The all cars figures cover all class 4 vehicles (cars and light vans) tested at the same age.
Looking at a Smart Forfour?
These figures describe the model, not the car in front of you. Found one you might buy? See what the VetTheCar Buying Report covers, or use the tools that work without a registration.
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Repair estimates: ONS consumer price quotes for local garage labour (09/2025 to 08/2026), the MOT inspection manual for defect wording, and estimated labour hours and parts bands. Not affiliated with or endorsed by ONS.
Source
Contains public sector information licensed under the Open Government Licence v3.0. Source: DVSA anonymised MOT test data, class 4 normal MOT tests, 2022 to 2025. MOT data updated 28 September 2026.
Not affiliated with or endorsed by DVSA. How we calculate these figures · Data sources