mechanics.tradeExhaust emissions
Testers wrote exhaust emissions down 436,271 times during 2025, 23rd on a list of 265 kinds of defect.
436,271recorded in 2025
1.4%of all recorded defects
23rdon the national list
What it is
A probe in the tailpipe measures what the engine is producing against limits set for that car's age and fuel. It is a measured test, taken with the engine fully warm.
What the tester can write down
| Wording on the certificate | Category | Recorded in 2025 |
|---|---|---|
| Lambda coefficient outside the default limits or the range specified by the manufacturer | Major | 178,731 |
What you can do about it
A good run at motorway speed beforehand genuinely helps, because the converter works properly only when hot. Persistent high readings usually point at a sensor rather than the converter itself.
Nearby on the list
Every defect on the list, from 42,728,066 MOT tests in 2025.