How to Lower Diesel Emissions for MOT

Since the EU Roadworthiness Package of May 2018, it has become a lot easier for diesel cars to fail their MOT. The level of nitrogen oxide (NOx) and carbon monoxide (CO) that diesel engines produce can have a detrimental impact on the environment and, consequently, the EU have put restrictions on the level of diesel emissions that your car can release.

The UK have mirrored this so currently, to pass your MOT, your car's MOT emissions have to fit specific criteria. Our tips will help you reduce your diesel car's NOx and CO emissions, not only saving you hundreds of pounds on a new vehicle, but also helping keep our planet safer for longer.

New Diesel MOT Emission Rules

In order to pass your MOT, your vehicle must adhere to a set of MOT emission rules. The MOT emission test rules in the UK state that:

Visible smoke must not come from the exhaust of your car
The Diesel Particulate Filter (DPF) must not have been removed or tampered with.
An engine management light - the light that signals there is a problem with the emissions system and/or DPF - must not be displaying
The emission restrictions for diesel engines must not be exceeded. The emission restrictions are as follows:
- CO limit of 0.50 gm/km
- NOx limit of 0.25 gm/km
- A combined HC and NOx limit of 0.30 gm/km
- PM limit of 0.025 gm/km.

How to reduce diesel emissions for MOT

If you have a diesel vehicle and you think it might not pass its MOT, there are a few things you can try before taking your car in:

Use premium fuel - premium fuel does tend to cost that extra bit more, but with good reason - it has ammonia added to remove any build-up of soot and dirt. Premium fuel will reduce your emissions as it cleans your fuel system, meaning you'll let off less poison into the environment
Check you have a DPF - if your car was made before 2011, it is very possible that you will not have a Diesel Particulate Filter (DPF) - diesel cars manufactured in the EU after 2011 are required to have a DPF. A DPF is a filter that catches the soot made from burning diesel, so ensuring you have one will help you pass your MOT. It is important to note that if your car already has a DPF, it is illegal to remove it; doing so could result in a £1,000 fine, failing your MOT and potentially invalidate your car insurance.
Install a SCR - a Selective Catalyst Reduction (SCR) adds ammonia to emissions, converting NOx to Nitrogen and Water Vapour, two substances that are already in the air. The SCR is one of the most effective ways of reducing NOx.
Tyre Pressure - keeping your tyres at the optimum pressure is a great way to reduce your NOx emissions. Deflated tyres require more turns to move your vehicle effectively meaning your car does more work and consequently burns more fuel. Pumping your tyres will help to reduce your diesel emissions and help pass your MOT.
Car Services - servicing your car regularly will keep you on top of your current MOT emissions and help you to make changes accordingly. If there are any problems causing you to use more fuel, then one of our mechanics will be able to spot it early and fix the problem - meaning you?re less likely to fail your MOT, and you?re helping to look after the environment