MOT failures by make
Smart MOT failures for “Catalyst emissions: Lambda reading after 2nd fast idle outside specified limits”
Smart cars failed their MOT on “Catalyst emissions: Lambda reading after 2nd fast idle outside specified limits” in 1.74% of 177,310 tests in 2023–2024 (3,077 tests) — 2.2 times as often as comparable cars of the same age, mileage and fuel, which would have failed on it in about 0.78% of tests. It is the number 8 most common failure item on Smarts.
Data to 2024-12-30 · Page updated 2026-09-28 · Publisher: 73 Auto
- Smart tests failing on it
- 1.74%
- 3,077 of 177,310 tests, 2023–2024
- Comparable cars
- 0.78%
- national rate at the same age, mileage and fuel
- Observed ÷ expected
- 2.22×
- 73 Auto analysis · rank #8 for Smart
How unusual this is for the make
Across all MOT failures, Smarts fail 1.06× as often as comparable cars. On this item the gap is 2.10× wider than that overall level, so it is a genuine Smart pattern rather than a reflection of how often the make fails in general. It is a major defect in the noise, emissions and leaks part of the test. Nationally it appears on 0.53% of MOT tests.
Smart models and “Catalyst emissions: Lambda reading after 2nd fast idle outside specified limits”
The Smart Forfour is most affected (3.71× comparable cars); the Smart Fortwo least (1.28×). Every model listed is above the national rate, so the pattern runs across the range. Model rows compare with cars of the same age and fuel.
| Model | Tests | Failed on it | vs similar cars |
|---|---|---|---|
| Smart Forfour | 48,547 | 2.13% | 3.71× |
| Smart Fortwo | 105,250 | 1.31% | 1.28× |
By age at test
The difference is largest at 7-8 years old: 2.59% of Smart tests against 0.45% for comparable cars.
| Age (years) | Smart tests | Smart | Comparable cars |
|---|---|---|---|
| 3-4 | 12,504 | 0.21% | 0.08% |
| 5-6 | 32,503 | 1.09% | 0.21% |
| 7-8 | 34,330 | 2.59% | 0.45% |
| 9-10 | 15,694 | 1.81% | 0.60% |
| 11-12 | 14,730 | 1.14% | 0.75% |
| 13-15 | 31,521 | 0.82% | 1.12% |
| 16+ | 34,183 | 3.21% | 1.73% |
Other Smart MOT faults that stand out
- Service brake performance: excessively binding · 1.71× comparable cars
- Washers: provides insufficient washer liquid · 1.52× comparable cars
Limitations
Official data: DVSA's anonymised MOT results (2023–2024), class 4 initial tests, cars at least 2.5 years old. 73 Auto analysis: the comparison rate applies the national rate of this item for each test's own age, mileage band and fuel to the Smart tests. An MOT result reflects maintenance, mileage and how a car is used as well as its design, so this is not a measure of which make is most reliable. The wording of the defect is DVSA's.
Has this Smart failed on it before?
Enter a registration to see that car’s own MOT history, advisories and the running costs 73 Auto expects. Your first check is free and shows the vehicle summary and its headline ownership cost. The category-by-category breakdown is part of a paid check.
UK number plate or 17-character VIN
Where these figures come from
- Anonymised MOT tests and results (2023 and 2024) — Driver and Vehicle Standards Agency (DVSA). Open Government Licence v3.0.
Figures labelled as 73 Auto estimates are our own analysis of these sources, set out in the methodology and data sources. To report a factual error, see corrections.