Changes to the 2018 MOT: diesel cars face stricter emissions test

Changes to the 2018 MOT: diesel cars face stricter emissions test

Changes to the MOT will come into force this May, making it more difficult for dirty diesel cars to pass air quality tests. A three-tier rating for the severity of faults on all cars will also be introduced.

The Driver and Vehicle Standards Agency (DVSA) claims the revisions to the MOT will make it tougher for anyone trying to cheat emissions tests and help keep vehicles in a dangerous condition off the road.

However, at the same time hundreds of thousands of cars more than 40-years old will no longer be required to take the annual road worthiness inspection. Here’s what motorists need to know about the changes.

Dirty diesels face stricter smoke test

We’ve all seen them: cars or commercial vehicles that belch out thick clouds of black smoke. Now the MOT is being toughened to remove vehicles with harmful pollution levels from the road.

Since 2014, MOT testers have had to check that a car’s original diesel particulate filter (DPF) – part of the exhaust system fitted to every new diesel from 2009 – is present. The aim was to deter the removal of the filters but testers didn’t have to see that it functioned correctly. That was a problem as DPFs often stop working properly.

Now a tougher emissions test means that a diesel with a DPF that ’emits smoke of any colour’ will automatically fail the MOT.

The DPF smoke test is an important step. Frank Kelly, professor of environmental health at Kings College London, says a car with a faulty or removed DPF has a particulate count 20 times higher than one with it.

New MOT defect categories


Cars over 40-years old: no MOT test required

Faults found during the new MOT test will be categorised in one of three areas, ranging from minor to dangerous. It will be for the tester to follow the correct procedures and standards when judging the severity of a problem. The faults are:

Minor defects: these have no significant effect on the safety of the vehicle or impact on the environment and other minor non-compliances. A test certificate will still be issued.

Major defects: these may affect the safety of the vehicle, have an impact on the environment or put other road users at risk. The car will fail its test.

Dangerous defects: they constitute a direct and immediate risk to road safety or the environment. The car will fail its test.

Cars over 40-years old: no MOT test required

From 20 May, most cars more than 40-years old will not need an MOT test.

However, the Department for Transport has included a caveat. This says any vehicle that has been ‘substantially changed’ must still be submitted for an MOT each year. And it still recommends regular maintenance and stresses the law requires all vehicles to be roadworthy.

This has led to confusion amongst classic cars owners. That’s because drivers need to understand the definition of ‘substantially changed’ to ensure they remain on the right side of the law.

If the technical characteristics of the main components have changed, the car will require an MOT. Replacing like with like is not considered a change.

The main components are the chassis or monocoque bodyshell, suspension or steering and engine.

Plans for the first MOT in fourth year dropped

A public backlash against plans to extend a car’s first MOT to its fourth year has led the government to abandon the idea.

Following overwhelming objection as part of a public consultation, a car will still require its first MOT at three-years old. Around 360,000 vehicles fail their first test each year.

10 comments on “Changes to the 2018 MOT: diesel cars face stricter emissions test

  1. Sam G January 31, 2018 9:53 am

    To all the people who mapped they cars and deleted dpf wish you all good luck.

    • MATTHEW January 31, 2018 12:07 pm

      The map shouldn’t be a problem if done correctly, however DPF delete is a totally different game, quite rightly so.

      • Thomas October 9, 2018 12:16 pm

        It is legal to have DFP delete? Saw some advantages and disadvantages. What do you recommend?

  2. Sam January 31, 2018 2:05 pm

    Why the manufacturers spend millions on Ecu programing and safe testing for engine longevity when Fred in the shed can do anything he wants and call it a remap there is no such thing as a safe map. Or even a right map it shortens the life of a engine plus all the problems e.g. Gear box clutches turbos injectoers unless you can prove it to me other wise

    • dervheid March 12, 2018 1:28 pm

      Hi Sam.
      Your clam: ergo the burden of proof is with you.

    • Ian Bruce March 14, 2018 10:17 pm

      With you all the way Sam. If people want the performance of a Porsche why the hell would you buy that Clio and then remap it and expect the performance of anything short of a eh umm Clio.

  3. James March 9, 2018 1:24 pm

    Unfortunately the poop is about to hit the fan for diesel drivers (and i am one too) The May 2018 MOT regs will fail a car where the emissions as measured at the exhaust pipe are not closely in line with the manufactures data plate attached to the car

  4. miike newby March 13, 2018 8:38 am

    So, owning a 2012 Renault 160cc Megane diesel reassures me a little. If the particulate filter is properly inspected and replaced if necessary, can I assume that my diesel is no more harmful than a large capacity petrol engine?

  5. Steve March 13, 2018 7:59 pm

    My car’s DPF became blocked with ash at around 90,000 miles and I paid over £1000 to have a new one fitted. It now goes into regeneration mode every 350 miles or so, at which time it emits grey smoke due to the injection of fuel into the system to burn off the soot. This is apparently what it is supposed to do.
    I will not be too pleased if this now considered to be a reason for failing an MOT and I have to scrap the car.
    Shame the manufacturer forgot to mention DPF issues when I bought it.

  6. jeff March 15, 2018 2:53 pm

    Of course we all believe that every car 40+ years old will be correctly maintained now they don’t have to have an MOT. Welcome back rotting chassis and bald tyres and brake shoes down to the rivets!

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