Motorists ‘unprepared’ for diesel vehicle MOT changes

A significant proportion of drivers are unprepared for changes to MOT tests which came into force yesterday (20 May), which will see more rigorous testing carried out on diesel vehicles, motoring body RAC has claimed.

The changes, which apply on cars tested in England, Scotland and Wales, affect the way that cars, vans, and other light passenger vehicles are tested, and see defects categorised as either ‘dangerous’, ‘major’ or ‘minor’ depending on the type of issue found.

MOT testing requirements have changed to include greater focus on diesel particulate filters

This includes tougher testing on diesel cars with a diesel particulate filter. A DPF captures and stores exhaust soot in order to reduce emissions from diesel cars, and is legally required to prevent the emission of high levels of particulates.

The filters have a finite capacity, which means that trapped soot has to be emptied or ‘burned off’ regularly to regenerate the DPF. Now, vehicles will get a major fault if the MOT tester can see smoke of any colour coming from the exhaust or finds evidence that the DPF has been tampered with.

However, according to RAC, which has canvassed over 1,800 motorists ahead of the MOT changes coming into effect, many drivers are unaware if their car is compliant with the requirements.


Up to half of motorists questioned (48%) in the RAC survey said they currently own, or run, a diesel car, and of those 53% said their car had a DPF.

However, more than a third (37%) didn’t know whether their vehicle had one or not.

According to RAC owners that find out at the time of their vehicle’s MOT that the DPF needs replacing could be in for a very nasty surprise as new ones often cost in excess of £1,000.

Additionally, RAC has claimed that many drivers are unaware of the potential cost of replacing their DPF, with 49% of diesel car drivers surveyed believing that a new filter is likely to cost between £250 and £500. Only 23% of respondents with diesel cars correctly realised tend to cost over £1,000 not including labour, RAC said.

RAC spokesman Simon Williams said:  “There is rightly a lot of attention at the moment on ‘harmful to health’ nitrogen dioxide emissions from diesel vehicles so stricter rules should help to make sure vehicles aren’t emitting more than they should be.

“Those unlucky enough to discover their vehicle has a faulty or tampered with diesel particulate filter will, unfortunately for them, be burning a big hole in their pocket due to the very high cost of replacement.

“Drivers who have a diesel vehicle with a DPF should make sure it is regularly given a good run at motorway or dual carriageway speeds so the filter is automatically cleared of any clogged up soot. This is very important if the vehicle is predominantly used for short journeys on local roads.”

In anticipation of the changes, the RAC has compiled guides to both the MOT changes and diesel particulate filters, which are available via its website.


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