The inspection measures exhaust emissions: carbon monoxide (CO) at idle for petrol cars and smoke opacity (light absorption coefficient, m⁻¹) for diesels. EU Directive 2014/45/EU sets these general limits:
- petrol cars with advanced emission control (catalytic converter and lambda sensor): CO at idle at most 0.3% (older cars 0.5%), at high idle 0.2% (older cars 0.3%);
- diesels first registered after 1 July 2008: smoke opacity at most 1.5 m⁻¹;
- older diesels: 2.5 m⁻¹ (naturally aspirated) or 3.0 m⁻¹ (turbocharged).
A manufacturer's value may apply to a specific car – it is shown on a plate under the bonnet or in the documents.
What do the CO and smoke figures on a model page show?
The median of all readings in that group and the share over the limit – for example Toyota Avensis 2008. Exceeding the limit usually counts as a major defect.
Why are petrol and diesel counted separately?
They measure different things, so medians are computed per fuel type. Every make page shows its fuel mix.