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Why do MOT tests include an exhaust emission test?​

9th January 2023

Why do MOT tests include an exhaust emission test? 

An exhaust emission test looks at the level of pollutants that are emitted from the exhaust of your car, with the aim to reduce the amount of harmful pollutants to the environment. Diesel and petrol emission tests are different but are both tested as part of an MOT. 

  • Petrol – the emission test measures gasses that exit the exhaust. 
  • Diesel – the emission test measures opacity using light. 

Emission tests are carried out to make sure that your vehicle’s engine is functioning efficiently so that any pollution created by the engine is kept to a minimum.  

How can I reduce my car’s emissions? 

Your car should be in line with what the manufacturer specifies in order for your car to be classed as in good working order. New vehicles are unlikely to fail their MOT, however, older cars that are diesel may fail their MOT based on high emission levels. There are ways that you can reduce your car’s emissions, such as: 

  • Change your fuel - albeit more expensive, using premium fuel can help reduce your car’s emissions due to being a better grade of fuel. This could save you money in the long run as the cleaning agents in premium fuel can help remove any build-up in your engine.  


  • Check your tyre pressure - under-inflated tyres are not only a danger to drive on, but they can also lead you to using more fuel which will increase emissions. We recommend that you ensure your tyres are set to the correct pressure to help reduce your emissions output. You can find the recommended tyre pressure for your vehicle in your vehicle handbook or on the inside of the fuel tank flap. 


  • Servicing your car regularly - we recommend regularly servicing your car to improve your vehicle’s emissions. This is because, during a service, your engine oil is changed to help keep your engine running effectively. Air filters are also changed, which can lower your emission output by removing any build-up that can impact the engine. 

Here at Merityre, all our specialists offer a range of car servicing options to cater for the needs of all motorists. Book in for a service at your local Merityre branch or contact our friendly team to find out more. Make sure to check out our gold club for a 10% discount on servicing and more – sign up today and start saving.