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The New MOT: Stricter Rules for Diesel Cars

Exhaust fumes from a muddy red car

If you’re not completely up-to-date with the latest news on our blog, you might not be aware of the upheaval caused by the new MOT test. The changes brought in with this new test will certainly make things more difficult for drivers across the UK. We’re going to take a closer look at the new, stricter MOT rules for diesel car drivers and how this will affect you.


What are the new MOT rules for diesel car drivers?

If you’ve not yet had the chance to get up to speed with the recent changes, read up on the MOT changes in 2018. To sum up, the new test has:

  • Renamed the pass and fail categories
  • Brought in in stricter rules for emissions
  • Included new items in the test
  • Changed the MOT certificate
  • Excluded older vehicles from MOT

While these changes will affect all drivers, it’s the stricter rules on emissions that are most significant for diesel car drivers. The new test urges greater scrutiny from MOT testers towards diesel car exhaust emissions. More specifically, testers will now have to closely check DPFs—a move that could cause many vehicles to fail their MOT tests and possibly cost drivers hundreds of pounds in repairs.

What is a DPF? Diesel cars produce a lot of soot which can pass into the atmosphere—causing pollution and respiratory problems. To combat this issue, modern diesel cars—from 2009 onward—now have Diesel Particulate Filters (DPFs). The DPF works by capturing and storing the soot produced by the car, thus stopping it from being released into the atmosphere.

You’ll get a major fault if…

  • The MOT tester can see smoke coming from your exhaust
  • If the tester finds evidence of tampering with your DPF

How will this affect me?

Airmen inspecting a car's engine

While DPFs are beneficial for diesel cars, many garages and drivers are guilty of tampering with them—or removing them entirely—to improve vehicle performance. The previous MOT test stipulated that testers should reject cars if their DPFs are missing completely. The new MOT test, however, has testers looking closely at DPFs to see if there are any signs of removal or tampering. Vehicles will also get an instant major defect if they emit any visible smoke of any colour.

If the tester does find evidence that your DPF has been tampered with, you could be fined £1,000 or more. And that’s not all—you’ll have to pay for the repair or replacement of your DPF. Depending on the price, diesel drivers could be £1,000£3,000 out of pocket by the end of the whole process. If your DPF has been repaired or replaced at any point in time, you’ll need to give the MOT tester evidence, e.g., a receipt.

Of course, if you’re lucky enough to have a vehicle built before the introduction of DPFs, you won’t have to worry about these changes.


How do I avoid getting a fail?

Hands with watch holding steering wheel

Don’t want to get pulled up on your MOT for a faulty DPF? Maintain it by ensuring it’s able to regenerate when it’s full of soot. Not sure how the process works? There are two types of regeneration: passive and active.

① Passive regeneration

This process occurs on the motorway where exhaust temperatures are higher than usual. This high temperature enables the DPF to passively regenerate by cleanly burning the excess soot in the filter. Diesel drivers should try to drive for 30 minutes or over at a sustained speed on the motorway to keep the filter clear.

Not a frequent motorway driver? This is where the second process comes in.

② Active regeneration

This process of regeneration involves the vehicle automatically sending more fuel to the engine. This is to increase the exhaust gas heat in order to burn the excess soot. If your journey is too short, however, the process won’t complete properly. In these cases, a warning light will pop up to show that the DPF is still blocked.

If your DPF is still blocked, you’ll need to get it fixed at a garage where they can implement a forced regeneration.


What’s the point?

So, why are the MOT rules for diesel car drivers stricter? It’s simple, really. The DVSA’s main priority is ensuring all road users are safe and that vehicles aren’t causing unnecessary damage to the environment. By pushing MOT testers to be stricter with DPFs, they’re limiting the damage caused by exhaust fumes to the atmosphere. These rules ensure all vehicles on the road are roadworthy—also giving greater clarity to drivers as to what constitutes as a defect.

Get ahead of the game and make sure your vehicle is up to scratch before your MOT test is due. You don’t want to pay for unnecessary fines or repairs, after all!

Don’t miss out on all the latest in the world of driving. Keep a close eye on the PassMeFast blog for news, driving tips and much more!

By Bethany Hall

Whether you’re a learner or a pro driver, Bethany is here to help. From defensive driving to the Highway Code, she’ll tell you everything you need know about driving. If she’s not on the road, you’ll probably find Bethany with her head in a book or binge-watching the latest TV show.

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