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How to reduce diesel emissions for MOT

15th May 2024

The exhaust emissions test forms one part of the MOT test. This requires your car to meet specific criteria for the number of emissions coming from your vehicle. Since May 2018, there has been a crackdown on the amount of diesel emissions released into the atmosphere. Merityre’s helpful article explains how to reduce diesel emissions to pass your MOT. 

What is the diesel emissions test? 

The diesel emissions test inspects the concentration and number of hydrocarbons and carbon monoxide released into the environment. If you have an old diesel vehicle, it’ll produce more emissions than a newer diesel car, thus increasing the chances of failing its MOT test. 

What are the requirements for MOT test emissions? 

When your diesel vehicle goes for its MOT, it must pass a series of legal requirements. If it does not meet these requirements, it’ll fail the MOT test. The standards regarding MOT emissions are: 

  • Your car must not have visible smoke coming from the exhaust. 
  • Your van or car must not exceed the petrol or diesel emission restrictions. 
  • Your vehicle’s diesel particulate filter must not be removed or tampered with. 
  • Your car must not display an engine management light, which signals an issue with the DPF and emissions system. 

Why are more diesel cars failing the MOT? 

One significant change to the UK’s MOT test was enforcing stricter rules around emissions, thus keeping it in line with the EU Roadworthiness Package. Since the criteria have been in place, diesel-powered vehicles have been impacted more than petrol-powered vehicles. More scrutiny is placed on the health of diesel engines, including: 

  • The engine management warning light. 
  • The diesel particulate filter. 
  • Visible tailpipe emission coming from the exhaust. 

How can I lower my diesel emissions for the MOT test? 

Have you got your MOT test coming up? Are you looking to reduce your diesel emissions? Our tips can ensure your diesel car passes its MOT every time: 

  • Changing your fuel – Swapping from standard fuel to premium diesel decreases the likelihood of chemicals entering the fuel tank, thus removing any dirt and debris you may experience with cheaper diesel. 
  • Installing a diesel particulate filter – Diesel cars manufactured after 2011 will have a DPF fitted. However, if you have a car manufactured before 2011, you should install a DPF. The DPF collects the soot from your exhaust, thus reducing harmful diesel emissions released into the atmosphere. If you remove your DPF from your car, you could receive a £1,000 fine, fail your MOT, and invalidate your car insurance. 
  • Check your tyre pressure – Having the wrong amount of pressure in your tyres can affect your car’s emissions. Underinflated tyres require more energy to turn the wheels and to maintain speed. Underinflated tyres will therefore contribute to higher fuel consumption. 
  • Use a selective catalytic reduction (SCR) system – A SCR is an advanced emissions control system that converts exhaust gases from nitric oxide (NOx) to nitrogen and water vapour. This is an effective way of reducing emissions from your diesel vehicle. 

Reducing your car’s diesel emissions will increase its chances of passing the MOT test.  If you want to know why MOT tests include an exhaust emission test, our article explores this topic in-depth. Ensure your diesel car passes its MOT test by booking an MOT test at your local Merityre branch today.