Stricter emissions tests for MOT drivers from May 2018

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What you need to know about the  New MOT rules

May 2018 will see a raft of changes to the annual MOT test that any vehicle over three years old must undergo. Among the changes are new fault categories and stricter emissions tests for diesel vehicles. This directive has been welcomed by many drivers following recent media coverage on the cleanliness of diesel cars and the safety of UK roads. So, what are the changes and how will they affect motorists?

A stricter smoke test

We’ve all seen cars and commercial vehicles on the road emitting clouds of black smoke. The new rules, however, will make this a thing of the past. These clouds are produced when a vehicle’s diesel particulate filter isn’t working efficiently, and results in up to 20 times more particulates being released into the air.  

It’s been the case since 2014 that cars and vans must retain their original DPFs. This rule was introduced following the discovery that many drivers were cheating the emissions test by removing faulty DPFs. Now, however, the filters will be checked for functionality as well as for presence in the vehicle, meaning that damage to, or lack of a DPF will result in immediate MOT failure.

Any smoke of any colour will mean failure, and evidence of a canister that has been cut and resealed could result in the tester refusing to test the vehicle. If the owner can prove that the damage was caused by an attempt to clean the filter, however, the car will be accepted.

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New MOT fault categories

In addition to the stricter smoke test, a set of fault categories is being introduced to identify the severity of any defects found during the test. This, of course, affects vehicles of any fuel type and takes a three-tiered format, encompassing:

Minor defects, which don’t pose a substantial risk to safety or the environment. If found, they are noted but the vehicle will pass its test.

Major defects are those which have a significant effect on vehicle safety or the environment, or which put other road users at tangible risk. If found, an MOT certificate will not be issued.

Dangerous defects are those which directly and immediately threaten road safety or the environment. If found, the vehicle will fail its test.

It is up to the tester to follow the given procedures and standards to determine the seriousness of a fault.

In classifying the defects found, it’s hoped that road safety will be improved. The failure of an MOT means that cars should not be driven until the relevant faults are fixed, and both testers and drivers are thus given more responsibility when it comes to safety on the roads.   

Vehicles of 40 years old or more

A final change is that from May, those seeking 40-year-old used cars for sale needn’t worry about the annual MOT. Cars of this age or older are not required to be tested, although changes to technical elements of the vehicle’s main components – namely the chassis, monocoque bodyshell, suspension, steering and engine –  do mean an MOT test is needed.



A former car magazine editor, Sophie’s blog offers in-depth car reviews, industry trends, and maintenance tips. Her breadth of knowledge makes her posts invaluable for both car enthusiasts and everyday drivers.

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