How to reduce diesel emissions for MOT

Tuesday 16th June 2020

What is the MOT emissions test?

As part of the UK’s MOT test, there is a strict exhaust emissions test which your vehicle needs to pass. This is primarily to adhere to the large worldwide focus to reduce pollution levels which are produced by diesel engines. In order to achieve this, certain limits have been introduced in order to ensure cars aren’t actively creating excessive emissions.

In May 2018, the emissions test was altered to adhere to the increasing concerns about the environment, and the affects diesel can have on our planet. This was as part of the EU Roadworthiness Package. The test measures the amount and concentration of carbon monoxide and hydrocarbons which are being released. The older your diesel vehicle, the more likely it is to produce a higher level of emissions. The test will measure the amount of carbon monoxide and hydrocarbons that your car is emitting, as these gasses are usually released from the exhaust pipe.

MOT emissions test rules

During an MOT test, the emissions test rules state that:

Your vehicle must not exceed the emissions restrictions for diesel engines.
Your vehicle’s Diesel Particulate Filter (DPF) must not have been removed or tampered with.
Your vehicle must not display an engine management light – as this light signals that there is a problem with the emissions system and/or DPF.
Your vehicle must not have visible smoke coming out from the exhaust.

How to pass diesel emissions test

Diesel engines produce nitrogen dioxide, and older diesel cars are more likely to fail their MOT because of this. There are few simple steps you can take to reduce diesel emissions on a diesel car:

Tyre pressure – did you know that having the correct tyre pressure can affect your diesel emissions? If your tyres are under inflated, this could increase your vehicle’s diesel emissions. This is because if the tyre does not have enough air in it, it may have to make an increased number of turns in order to get your vehicle to move effectively, which then increases your fuel usage. Learn more about checking your vehicle’s tyre pressure.
Using premium fuel – premium fuel is well known for lowering vehicle emissions. Cheaper fuel is likely to lack the added chemicals which remove build-ups of soot and other dirt and debris – which is a key advantage of premium fuel, effectively cleaning your car’s engine and lowering diesel emissions.
Install a SCR – a Selective Catalytic Reduction (SCR) refers to an advanced active emissions control technology system which converts your exhaust gases from NoX to nitrogen and water vapour. This can be extremely effective for reducing emissions of your vehicle – as it adds ammonia to the exhaust gases through a special catalyst in the exhaust stream.
Install a DPF – a Diesel Particulate Filter (DPF) is a filter which catches the soot from your exhaust – helping to reduce emissions from diesel cars. Just ensure you regularly clean the filter every so often! However, any EU diesel cars manufactured after 2011 will now already have DPF installed when you buy the vehicle – so you don’t need to worry. Although, it’s important to note that it’s illegal to remove your DPF – and you could receive a fine of up to £1,000 for doing so, while also potentially invalidating your car insurance.
Regular oil checks – whether you require regular oil or a specialist oil supplement, keeping on top of your oil in your vehicle is likely to ensure your vehicle is in good shape for both emissions and efficiency.
Regular car services – keeping your car regularly serviced is not only beneficial to passing your diesel emissions test, but also keeping on top of your general car maintenance. Find out how regular car services can save you money now.

Now you know how to reduce diesel emissions for MOTs, perhaps you’re ready to book in for your MOT test online? Locate your nearest test centre or get in touch with a member of our expert team today.