Which? tests show almost 80% of diesels exceed emissions limits

Which? has found that almost 80% of diesels it has driven exceed the official emissions limits when put through real-world tests.

The consumer advice service has tested 61 diesel cars since the start of 2017, and found that 47 (77%) of them exceed the Euro 6 NOx emissions limit of 0.08 g/km - despite having a Euro 6 certified engine.

The average NOx figure from Which?'s diesel tests is 0.27 g/km, more than three times the official limit, and the worst results from its testing programme come from the Subaru Forester. This produces 2.0 g/km NOx when subjected to cycles based on real-world testing according to Which?, 25 times the official limit.

All five diesel Renault cars tested by Which? during this timeframe are in the top 10 worst performing models in terms of NOx emissions, including the Grand Scenic and Captur in second and third place behind the Forester.

At the other end of the table, BMW and Mercedes Benz score particularly well. So well in fact that the Mercedes E 220d - producing 0.023 g/km NOx - had such a surprisingly low result, the testing team took the car out of the laboratory and on to the road to see if there was a problem with the programme. Figures from a Portable Emission Measuring System (PEMS) nearly matched the lab figures.

The variances come about for a number of reasons. The primary difference is that Which? is carrying out tests using real-world conditions as the base of its protocols, rather than the NEDC standards. The NEDC test is outdated to the extent the industry is starting to switch over to a new WLTP system, and is also based in a laboratory.

Which? tests are also carried out in laboratory conditions, though the cars are run in the default setting they start up in - no switching to eco mode for example if the car isn't already there. All test cycles are also conducted with air conditioning on, dipped headlights, and the radio on.

The tests also include a motorway cycle, which the official tests don't, and the cars have a 200kg payload. By the time the WLTP figures become the official quoted test results, Which? reckons that 28 out of 61 diesel cars tested would meet the new NOx limits.

Having contacted the manufacturers singled out above, Which? reports that: "Groupe Renault said that while all its vehicles conform to applicable laws and standards, it's aware that there remains significant potential for improving the level of NOx in real-use conditions."

Mercedes Benz has replied with: "For premium vehicles, from our perspective, the diesel has definitely a future. Therefore, Daimler AG [owner of Mercedes] has invested about 3 billion Euros into the development and production of a completely new diesel engine family.

"Our new engines are both highly efficient and produce low levels of NOx. It is a fact that it is worth improving the modern diesel instead of banning it."

Subaru has not replied to Which?'s request for a comment at the time of going to press. The complete results of diesel models tested are listed below.

Model Engine & trim Which? NOx (g/km)
Subaru Forester (2013-present) 2.0D Sport Lineartronic 2.022
Renault Grand Scenic (2016-present) Energy DCI 160 Bose Ed EDC 0.896
Renault Captur (2013-present) dCi 90 Intens 0.725
Peugeot 5008 (2017-present) BlueHDi 150 Allure 0.7
Ford Kuga (2012-present) 2.0 TDCI S/S Vignale 4x4 0.655
Renault Megane (2016-present) dCi 130 GT Line 0.504
Kia Sorento (2015-present) 2.2 CRDI GT Line AWD Auto 0.48
Renault Scenic (2016-present) Energy DCI 110 Hybrid Assist Intens 0.478
Renault Scenic (2016-present) Energy DCI 130 Bose Edition 0.472
Ssangyong Korando (2011-present) 2.2 e-XDi 220 Sapphire 4Wd Auto 0.468
Citroen SpaceTourer (2016-present) M BlueHDi 150 S/S Shine 0.436
Kia Sportage (2016-present) 2.0 CRDI 136 Spirit AWD 0.427
Kia Optima Sportwagon (2016-present) 1.7 CRDI GT-Line DCT 0.4
Fiat Tipo (2016-present) 1.6 Multijet S/S Lounge 0.383
Ford Edge (2015-present) 2.0 TDCI BiTurbo S/S Titanium 4x4 Powershift 0.38
Alfa Romeo Giulia (2017-present) 2.2 Diesel Super AT8 0.376
Mercedes Benz CLA Shooting Brake (2015-present) 200 d 136hp 2WD 0.357
Mazda CX-5 (2017-present) Skyactiv-D 150 Exclusive Line 0.342
Mazda 3 (2013-present) Skyactiv-D 105 Sports Line 0.329
Hyundai i40 Tourer (2011-present) 1.7 CRDi blue Premium DCT (2016) 0.313
Vauxhall Insignia Sports Tourer (2017-present) 1.6 Ecotec Diesel s/s business innovation 0.302
Land Rover Discovery Sport (2015-present) TD4 E-Capability HSE 0.3
Volkswagen Golf SV (2014-present) 1.6 TDI BMT Comfortline 0.299
Volvo V90 Estate (2016-present) D5 Inscription AWD Automatic 0.267
Peugeot 3008 (2016-present) BlueHDI 120 Allure 0.266
Nissan Qashqai (2014-present) 1.6 dCi Tekna 0.24
Alfa Romeo Stelvio (2017-present) 2.2 diesel Super Q4 AT8 0.228
Audi A5 Cabriolet (2017-present) 2.0 TDI design quattro S tronic 0.22
Skoda Octavia VRS Estate (2013-present) RS TDI DSG 0.219
Jaguar F-Pace (2016-present) 20d Prestige AWD Automatic 0.215
Volvo S90 (2017-present) D4 Inscription Auto 0.191
Audi Q7 e-tron (2016-present) e-tron quattro tiptronic 0.177
Skoda Kodiaq (2017-present) 2.0 TDI SCR style 4x4 DSG 0.172
BMW 3-Series GT (2013-present) 320d Gran Turismo Luxury line steptronic 0.166
Audi Q5 (2017-present) 2.0 TDI design quattro S-tronic 0.131
Audi SQ7 (2016-present) SQ7 TDI Quattro Tiptronic 0.123
BMW 5 Series Touring (2017-present) 530d Touring Sport Line Steptronic 0.122
Ford Fiesta (2017-present) 1.5 TDCi s/s Titanium 0.116
BMW 3-Series (2012-present) 318d Touring Steptronic 0.114
Mercedes-Benz GLC (2015-present) 220d 4Matic 9g-tronic 0.112
Mini Countryman (2017-present) Cooper D 0.107
Mercedes-Benz GLC Coupe (2016-present) 250d 4matic 9g-tronic 0.099
DS 7 Crossback (2017-present) BlueHdi 180 Automatic 0.098
Volvo XC60 (2017-present) D5 R Design AWD Geartronic 0.093
Vauxhall Insignia Grand Sport (2017-present) 2.0 Diesel s/s Business Innovation 0.087
Volkswagen Arteon (2017-present) 2.0 TDI SCR Elegance 4Motion DSG 0.087
Volkswagen Passat Estate (2015-present) 2.0 TDI SCR BMT Highline 0.084
BMW 7-series (2015-present) 730d Steptronic 0.08
Vauxhall Zafira Tourer (2012-present) 2.0 CDTI ecoflex s/s innovation 0.076
Seat Ateca (2016-present) 2.0 TDI Xcellence 4Drive DSG 0.076
Land Rover Discovery (2017-present) TD6 SE Automatic 0.061
BMW 5-series (2017-present) 520d Luxury Line Steptronic 0.053
BMW X3 (2017-present) xDrive20d xLine Steptronic 0.043
Mercedes-Benz CLS (2018-present) 400d Coupe AMG Line 4Matic 9GTronic 0.042
Peugeot 308 SW (2014-present) 2.0 BlueHDI 180 GT EAT8 0.041
Mercedes-Benz S-Class (2013-present) 400d 9G-Tronic 0.035
Vauxhall Grandland X (2013-present) 2.0 Diesel s/s Innovation Automatic 0.034
BMW X2 (2018-present) xDrive20d M Sport X Steptronic 0.031
Mercedes-Benz E-Class Estate (2016-present) E220d 9g tronic 0.028
Mercedes-Benz E-Class (2016-present) E220d 9g tronic 0.024
BMW 2 Series Active Tourer (2014-present) 218d Steptronic 0.014

Find out more about emissions here

Chris Lilly

Author:Chris Lilly
Date Updated:16th Aug 2018

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