Petrol cars twice as likely as diesels to fail MOT emissions tests

Wednesday, November 6, 2013 - 10:00
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MOT: Emissions cause one in four failures

Petrol cars are twice as likely to fail MOT emissions tests as their diesel counterparts, new data has shown.

Excess exhaust emissions levels account for 26.2% of all MOT failures, with 9.7% of petrol cars tested failing compared to just 3.9% of tested diesel cars.

The figures, released by Redex, also show 47.97million MOT tests were taken between January 2010 and September 2011, with 14.43million failure reasons recorded.

Of these failure reasons 3.78million were attributed to emissions that exceeded permitted levels.

Bruce Ellis, Research and Development Manager at Redex, said:  “There are a number of possible explanations for the marked difference in MOT emissions failure rates between petrol and diesel cars.

“These include the different driving cycles that traditionally are undertaken.

“Namely, petrol cars are more likely than diesels to be chosen for frequent shorter, urban trips, whereas diesels are more likely to be chosen if the vehicle is to be commonly used for longer, motorway-based journeys.

“Also, diesels operate at lower engine speeds and are therefore a little less stressed than higher revving petrol motors.

“But the most obvious explanation is likely to be the MOT test itself.

“Petrol cars are assessed for a high number of gases and hydrocarbons in the exhaust emissions, while diesels are tested only for smoke levels.

“This means that relatively speaking, diesels probably have an easier emissions test than petrol-engined cars.”

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