Technician carries out emissions MOT testTechnician carries out emissions MOT test


Diesel MOT failures up by 240 per cent since tougher emissions test is introduced

Time 4 months ago

An investigation has found that tougher emissions tests at MOTs led to 76 per cent more vehicles failing their while diesels were hit hardest, failing 240 per cent more.

The staggering figures saw the number of failures shoot from 745,308 in 2017-2018 to 1,311,841 the following year, when the MOT changes came in on May 20.

A Freedom of Information request to the DVSA revealed that this number remained nearly as high in 2019-2020, up by 70 per cent compared to before the new rules were introduced and reaching 1,272,771 failures.


In 2018, new rules were introduced to clamp down on excessive exhaust emissions and cars with diesel particulate filters (DPF) would fail if it was found to be tampered with.

In the same regulations update, the DVSA introduced new fault categories where ‘major’ or ‘dangerous’ would also lead to a failed test.

Diesel vehicles have seen the biggest impact, largely from emissions. The failure number increased by 240 per cent last year compared to two years before.

Petrol failures only increased by a third but nearly all were classed as ‘major’, while five per cent of diesel failures were classed as ‘dangerous’.


SMMT figures show the market share of diesel cars accounted for just 16 per cent of new car sales last year. In 2015, about 50 per cent of new cars sold were diesel.

Jessica Potts, head of marketing at BookMyGarage who requested the information, said: ‘The regulations have mostly impacted diesel cars, causing more than triple the number to fail, compared to petrol car failures which have only increased by a third.’

She added: ‘Since the Volkswagen ‘dieselgate’ scandal in 2015, diesel cars have earned a bad reputation for producing harmful exhaust emissions.

‘That’s not to say all diesels are bad. The latest diesel cars are equipped with emissions control systems such as particulate filters and selective catalytic reduction (AdBlue) to reduce or eliminate harmful emissions.

‘What this data tells us though, is that an increasing number of relatively modern diesels are struggling to pass the MOT test as their emissions control systems face tougher scrutiny. It’s important these systems function correctly to protect the environment, but putting them right can also cost owners thousands of pounds.’

Rebecca Chaplin's avatar

Rebecca has been a motoring and business journalist since 2014, previously writing and presenting for titles such as the Press Association, Auto Express and Car Buyer. She has worked in many roles for Car Dealer Magazine’s publisher Blackball Media including head of editorial.

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