What's the focus on diesel cars for?

A crackdown on diesel car emissions is evident in the new test. If your diesel car puts out any smoke whatsoever, it won’t pass its MOT examination.

Testers are also being told to do thorough checks of a car’s DPF (Diesel Particulate Filter) to ensure that they haven’t been tampered with – or removed entirely. The guidelines read that: “Any vehicles fitted with a DPF should be checked so that ‘no visible smoke is emitted from the exhaust during the metered check’.”

Some diesel drivers remove the filter to boost performance and increase miles-per-gallon, but since it regulates the exhaust gases produced by the engine, this isn’t the most ecological option.

It means that if a car was fitted with a DPF as standard, its removal would mean an instant MOT fail.

Since some drivers remove the internals of the DPF but keep the housing in place, testers are also being asked to check for tampering. That means that if there is any sign that the DPF has been disassembled and then welded back together, the car will fail the test.