Nearly 80% of diesel cars exceed emissions limit in latest Which? tests

By agency reporter
August 18, 2018

Most modern diesel cars are much dirtier than official limits, according to ongoing Which? tests that show the majority exceed official emissions limits when put through more rigorous real-world tests.

Which? has tested 61 modern diesel cars since the start of 2017, and found 47 of them (77 per cent) exceeded the Euro 6 limit of 0.08g/km of NOx (oxides of nitrogen), despite conforming to the official standards.

On average, the diesel cars tested under Which?’s current test programme produce 0.27g/km of NOx – nearly three and a half times the existing official Euro 6 limit. 

The worst culprit among these was the Subaru Forester (2013-present) which produced 2.0g/km of NOx, a shocking 25 times the Euro 6 limit that it met in official tests.

All five diesel Renault cars tested by Which? since the start of 2017, including the mild diesel hybrid, appear in the top ten most NOx emitting cars. The two Renault vehicles which come second and third in the table are the Grand Scenic (Energy DCI 160 Bose Edition EDC)  which recorded 0.896g/km of NOx in Which? tests and the Captur (dCi 90 Intens) which produced 0.725g/km.

In stark contrast, Mercedes has produced some cars with extremely low NOx emissions. The current E-Class diesel tested by Which? (specifically the 2.0-litre four-cylinder E220d 9G-Tronic diesel engine) produced just 0.023g/km of NOx. The result was so surprising that Which? experts took it out of the lab and onto the road to see how the figures compared, but the figures shown on the Portable Emission Measuring System nearly matched the lab figures.

Additionally, Which? found that the BMW 2 Series Active Tourer (specifically the 218d Active Tourer Steptronic diesel engine) produced just 0.014g/km of NOx.

Which? car testing is more rigorous than the official tests, with vehicles tested in the default setting in which they start up, rather than switching to a more economical driving mode.

Alex Neill, Which? Managing Director of Home Products and Services, said: “The current official tests fail to measure the actual level of emissions that cars are producing on our roads 

“Most diesels we assess are producing far more NOx in our tests than official limits allow. The new official tests should help reduce harmful emissions – but we will continue to penalise any car we find that produces excessive levels of pollutants in our tests.”

NOx (oxides of nitrogen) is comprised of NO (Nitrogen Oxide) and NO2 (Nitrogen Dioxide). NOx is harmful and has been linked to tens of thousands of premature deaths around the world. It comes out of all diesel, petrol and hybrid cars but in the latest tests diesel engines still produce an average of 11.5 times the amount of NOx compared with petrol cars.

* Which?



Although the views expressed in this article do not necessarily represent the views of Ekklesia, the article may reflect Ekklesia's values. If you use Ekklesia's news briefings please consider making a donation to sponsor Ekklesia's work here.