Does the Smart Forfour fail the MOT on noise, emissions and leaks more than it should?
The Smart Forfour records 3.78 noise, emissions and leaks failure items per 100 initial MOT tests (2019–2024), against 2.39 expected for a car of the same age mix: more than expected for its class and age (+1.39, 95% interval +1.29 to +1.50). It ranks 116 of 678 models on noise, emissions and leaks (1 = most failures above expected).
Data release dvsa-2024-v2 (24 Sep 2026) · page updated 30 Sep 2026 · all models on noise, emissions and leaks · check a Smart Forfour by registration
What exactly fails on noise, emissions and leaks?
The most frequent DVSA defect wording in this group on the Smart Forfour is “Lambda coefficient outside the default limits or the range specified by the manufacturer”, recorded 1,841 times in 2019–2024.
| DVSA defect wording | Items | Per 100 tests |
|---|---|---|
| Lambda coefficient outside the default limits or the range specified by the manufacturer | 1,841 | 1.35 |
| Engine MIL illuminated indicating a malfunction | 1,158 | 0.85 |
| Emissions levels exceed default limits | 619 | 0.45 |
| Emissions test unable to be completed | 532 | 0.39 |
| Emissions levels exceed the manufacturer's specified limits | 429 | 0.32 |
Source: DVSA MOT bulk data (OGL v3.0) · Window: 2019–2024 · n = 136,129 (initial tests) · Method: failure items (major and minor) grouped by DVSA's defect tree; wordings with 30+ items · Updated: 30 Sep 2026 · Release: dvsa-2024-v2 · CSV
If a Smart Forfour gets a noise, emissions and leaks advisory, how often does it fail next time?
7.7% of Smart Forfour MOTs with a noise, emissions and leaks advisory were followed by a fail in the same group at the next MOT, typically 12.1 months and 3,468 miles later (1,439 advisories followed).
Source: DVSA MOT bulk data (OGL v3.0) · Window: 2019–2024 · n = 1,439 (advisories followed) · Method: the same vehicles followed to their next ordinary MOT · Updated: 30 Sep 2026 · Release: dvsa-2024-v2 · CSV
Other pages for this model
Smart Forfour 2004 · Smart Forfour 2005 · Smart Forfour 2006 · Smart Forfour 2007 · Smart Forfour 2015 · Smart Forfour 2016 · Smart Forfour 2017 · Smart Forfour 2018 · Smart Forfour 2019 · Smart Forfour in Finland · Smart Forfour in the Netherlands · Smart Forfour by postcode area · Smart Forfour body, chassis and structure failures · Smart Forfour brakes failures · Smart Forfour vehicle identification failures · Smart Forfour lamps, reflectors and electrics failures · Smart Forfour road wheels failures · Smart Forfour seat belts and airbags failures · Smart Forfour steering failures · Smart Forfour suspension failures · Smart Forfour tyres failures · Smart Forfour visibility failures