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Consultation launched on changing the exhaust emissions test for light diesel engine vehicles

MOT test centre in Northern Ireland

The Department for Infrastructure (DfI) has launched a consultation on changing the annual roadworthiness test (MOT test) by introducing an alternative exhaust emissions test for cars and light goods vehicles fitted with a modern diesel engine.


Modern diesel engines may produce high levels of hazardous particulate matter if not properly maintained, and the current diesel smoke test is ineffective at detecting this. 



The PN test should take no longer to conduct than the existing petrol emissions test and, on that basis, no related test fee increase is envisaged at this time.


The eight-week public consultation proposes conducting an exhaust emissions Particle Number (PN) test on cars and light goods vehicles (first registered from 1 January 2013) fitted with a modern diesel engine, as a more effective alternative to the smoke opacity (density) test.


The relevant legislation will need to be amended to introduce this new diesel emissions test for light vehicles.



DfI is also proposing to change the legislation to include vehicles over 3500kg gross vehicle weight. This is to allow roadside enforcement checks to be carried out on modern light and heavy diesel vehicles to determine the effectiveness of the vehicle’s diesel particulate filter (DPF).


Following the consultation, all responses will be analysed before recommendations are made to the Minister for Infrastructure.


The public consultation is available here:




The proposed change to the annual roadworthiness test (MOT test) will provide for conducting the more effective exhaust emissions Particle Number (PN) test on cars and light goods vehicles (first registered from 1 January 2013) fitted with a modern diesel engine, as an alternative to the required smoke opacity (density) test.


The legislative change will also provide for similar emissions tests to be conducted during roadside enforcement checks on all modern light and heavy diesel vehicles to determine the effectiveness of the vehicle’s Diesel Particulate Filter.

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