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Tests by consumer organisation Which? have found that a large number of new diesel cars still exceed the new, tougher emissions limits in “real-world” testing.

Much fanfare has been made about the new WLTP and RDE fuel economy and emissions tests that were introduced by the EU last year, and which will apply to all new cars from this September. But based on the Which? research, a number of car manufacturers are still exploiting weaknesses in the testing procedures to build cars that pump far more toxins into the air than they should.

The tests have found that although some petrol cars produce excessive emissions when put through more rigorous testing than the EU requires, it is new diesel cars that are still spewing the highest levels of pollution from their exhausts.

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Confirming what we already knew

Based on the outgoing NEDC emissions limits, Which? found that a whopping 77% of new diesel cars tested in the last 18 months exceeded the legal emissions limits when put through more rigorous testing. In reality, this is hardly news anymore – we’ve known since before the Volkswagen Dieselgate scandal broke that manufacturers had been gaming the emissions regulations for years.

The official government fuel economy numbers were a joke, and therefore emissions were as well, because the official NEDC tests simply weren’t tough enough (and yet Volkswagen still couldn’t build engines that could pass these basic tests without cheating…).

But all this was supposed to come to an end with the new, tougher WLTP laws. It was claimed that manufacturers wouldn’t be able to outwit the new tests, so the results would be truly representative of what buyers could expect when they bought a new car. Every new model released since September 2017 has had to comply with the new rules, and by September 2018 (just two weeks away as this is written) all new cars on sale must comply. So, good news all round, right?

Diesel cars still poisoning our air

Sadly, no. Which? claims that more than half of the new diesel cars they have tested in recent months still pump out far more pollution than the new rules allow, because those new rules still don’t properly represent real-world driving in sensible real-world conditions.

The test protocols used by Which? are stricter than the EU’s new scheme, yet they are hardly unrealistic. For example:

  • Cars are tested in the default setting they start up in, rather than switching them to an ‘eco mode’ as the EU allows manufacturers to do for official tests.
  • All test cycles are conducted with the air conditioning, headlights and radio switched on.
  • In addition to running the EU’s new WLTP test, Which? also conducts a proper motorway cycle, which official tests do not have.
  • Cars are tested with a 200kg payload, which is roughly equivalent to two adults, a bit of luggage and a tank of fuel.
  • The tests are lab-based, but if the results seem suspicious, the car is driven on real roads and emissions are measured using a PEMS (portable emission measuring system).

Which? has tested 61 new diesel models using these protocols since the start of 2017. 47 of those 61 cars (77%) failed to meet the outgoing NEDC emissions requirements. 33 out of the 61 cars (54%) failed to meet the new WLTP emissions standards.

So how can these offending cars be allowed on sale?

The government tests are softer than the Which? tests, so manufacturers still have wiggle room to ‘optimise’ their vehicles for best possible results. And, obviously, they do everything they can to get the best results – even though they know the results will not be realistic.

They can switch the car into an eco mode (that most drivers never use because it makes the car sluggish and unresponsive to drive). They are allowed to turn off air-conditioners, radios, headlights and anything else that may use fuel. They don’t have to account for passengers, luggage or any fuel in the tank beyond what’s needed to complete the test. They can pump up the tyres way past a comfortable or safe level to reduce rolling resistance. Plus various other tricks and ploys.

All of these little loopholes add up to big differences in the final results, but the level of variation reported by Which? is astonishing. We’ve republished their full table below. The worst offender – the Subaru Forester – was found to be producing 25 times the legal emissions levels, yet still passed the old NEDC tests.

Subaru Forester diesel
The Subaru Forester diesel was the worst-polluting car tested by Which?

How does your car rate?

Here is the list of cars tested by Which? and their results. We’ve added columns to show how they rate against the old (NEDC) and new (WLTP) tests.

The new legal emissions limit from now until 2020 is actually double the current standard, as a sop to manufacturers from the EU for making the tests tougher. From 2020, the levels will decrease by 40%, although that still makes them 50% higher than the old NEDC levels.

Cars that fail both the old and new emissions standards under Which? testing
Fuel typeCar name and generationEngine/trimNOx (g/km)NEDC (0.08g/km)WLTP (0.168g/km)
DieselSubaru Forester (2013 to present)2.0D Sport Lineartronic2.0222428%1104%
DieselRenault Grand Scenic (2016 to present)Energy dCi 160 Bose Edition EDC0.8961020%433%
DieselRenault Captur (2013 to present)dCi 90 Intens0.725806%332%
DieselPeugeot 5008 (2017 to present)BlueHDi 150 Allure0.700775%317%
DieselFord Kuga (2012 to present)2.0 TDCI S/S Vignale 4×40.655719%290%
DieselRenault Megane (2016 to present)dCi 130 GT Line0.504530%200%
DieselKia Sorento (2015 to present)2.2 CRDi GT Line AWD automatic0.480500%186%
Diesel mild hybridRenault Scenic (2016 to present)Energy dCi 110 Hybrid Assist Intens0.478498%185%
DieselRenault Scenic (2016 to present)Energy dCi 130 Bose edition0.472490%181%
DieselSsangYong Korando (2011 to present)2.2 e-Xdi 220 Sapphire 4WD automatic0.468485%179%
DieselCitroën SpaceTourer (2016 to present)M BlueHDi 150 s/s Shine0.436445%160%
DieselKia Sportage (2016 to present)2.0 CRDi 136 Spirit AWD0.427434%154%
DieselKia Optima Sportwagon (2016 to present)1.7 CRDi GT-Line DCT0.400400%138%
DieselFiat Tipo (2016 to present)1.6 Multijet s/s Lounge0.383379%128%
DieselFord Edge (2015 to present)2.0 TDCi BiTurbo S/s Titanium 4×4 Powershift0.380375%126%
DieselAlfa Romeo Giulia (2017 to present)2.2 Diesel Super AT80.376370%124%
DieselMercedes-Benz CLA Shooting Brake (2015 to present)Diesel 2.1 (136bhp) 2WD0.357346%113%
DieselMazda CX-5 (2017 to present)Skyactiv D 150 Exclusive line0.342328%104%
DieselMazda 3 (2013 to present)Skyactiv D 105 Sports line0.329311%96%
DieselHyundai i40 Tourer (2011 to present)1.7 CRDi blue Premium DCT (2016)0.313291%86%
DieselVauxhall Insignia Sports Tourer (2017 to present)1.6 Ecotec Diesel s/s Business Innovation0.302278%80%
DieselLand Rover Discovery Sport (2015 to present)TD4 E-Capability HSE0.300275%79%
DieselVolkswagen Golf SV (2014 to present)1.6 TDI BMT Comfortline0.299274%78%
DieselVolvo V90 (2016 to present)D5 Inscription AWD automatic0.267234%59%
DieselPeugeot 3008 (2016 to present)BlueHDi 120 Allure0.266233%58%
DieselNissan Qashqai (2014 to present)1.6 dCi Tekna0.240200%43%
DieselAlfa Romeo Stelvio (2017 to present)2.2 diesel Super Q4 AT80.228185%36%
DieselAudi A5 Cabriolet (2017 to present)2.0 TDI design quattro S tronic0.220175%31%
DieselSkoda Octavia vRS estate (2013 to present)RS TDI DSG0.219174%30%
DieselJaguar F-Pace (2016 to present)20d Prestige AWD automatic0.215169%28%
DieselVolvo S90 (2016 to present)D4 Inscription automatic0.191139%14%
Diesel plug-in hybridAudi Q7 e-tron (2016 to present)e-tron quattro tiptronic0.177121%5%
DieselSkoda Kodiaq (2017 to present)2.0 TDI SCR Style 4×4 DSG0.172115%2%
Cars that pass the new WLTP emissions standards but fail the old NEDC standards
DieselBMW 3 Series GT (2013 to present)320d Gran Turismo Luxury line steptronic0.166108%-1%
DieselAudi Q5 (2017 to present)2.0 TDI design quattro S-tronic0.13164%-22%
DieselAudi SQ7 (2016 to present)SQ7 TDI quattro tiptronic0.12354%-27%
DieselBMW 5 Series Touring (2017 to present)530d Touring Sport Line steptronic0.12253%-27%
DieselFord Fiesta (2017 to present)1.5 TDCi s/s Titanium0.11645%-31%
DieselBMW 3 Series Touring (2012 to present)318d Touring steptronic0.11443%-32%
DieselMercedes-Benz GLC (2015 to present)220d 4Matic 9G-tronic0.11240%-33%
DieselMini Countryman (2017 to present)Cooper D Countryman0.10734%-36%
DieselMercedes-Benz GLC Coupe (2016 to present)250d 4matic 9G-tronic0.09924%-41%
DieselDS 7 Crossback (2017 to present)BlueHDi 180 automatic0.09823%-42%
DieselVolvo XC60 (2017 to present)D5 R Design AWD Geartronic0.09316%-45%
DieselVauxhall Insignia Grand Sport (2017 to Present)2.0 Diesel s/s Business Innovation0.0879%-48%
DieselVolkswagen Arteon (2017 to present)2.0 TDI SCR Elegance 4Motion DSG0.0879%-48%
DieselVolkswagen Passat estate (2015 to present)2.0 TDI SCR BMT Highline0.0845%-50%
Cars that pass both the old and new emissions standards
DieselBMW 7 Series (2015 to present)730d Steptronic0.0800%-52%
DieselVauxhall Zafira Tourer (2012 to present)2.0 CDTI ecoflex s/s innovation0.076-5%-55%
DieselSEAT Ateca (2016 to present)2.0 TDI Xcellence 4Drive DSG0.076-5%-55%
DieselLand Rover Discovery (2017 to present)TD6 SE automatic0.061-24%-64%
DieselBMW 5 Series (2017 to present)520d Luxury Line Steptronic0.053-34%-68%
DieselBMW X3 (2017 to present)xDrive20d xLine Steptronic0.043-46%-74%
DieselMercedes-Benz CLS (2018 to present)CLS400d Coupe AMG Line 4Matic 9G-tronic0.042-48%-75%
DieselPeugeot 308 SW (2014 to present)2.0 BlueHDi 180 GT EAT80.041-49%-76%
DieselMercedes-Benz S-Class (2013 to present)S400d 9G-tronic0.035-56%-79%
DieselVauxhall Grandland X (2017 to present)2.0 Diesel s/s Innovation automatic0.034-58%-80%
DieselBMW X2 (2018 to present)xDrive20d M Sport X Steptronic0.031-61%-82%
DieselMercedes-Benz E-Class estate (2016 to present)E220d 9G-tronic0.028-65%-83%
DieselMercedes-Benz E-Class saloon (2016 to present)E220d 9G-tronic0.024-70%-86%
DieselBMW 2 Series Active Tourer (2014 to present)218d Active Tourer Steptronic0.014-83%-92%


As you can see, the Subaru Forester is the worst of all, exceeding the current limits by more than 2400% (in other words, it produces about 25 times the legal limit) and exceeds the new limits by 1100% (about 12 times the new limit). It also produced more than double the emissions of the second-worst car, the Renault Grand Scenic. Renault also has five cars in the ten worst offenders.

At the other end of the scale, the BMW 2 Series Active Tourer and Mercedes-Benz E Class are model citizens. Which? was so surprised by the big Mercedes’ outstanding score that it put the E-Class through the RDE road test protocol to check it against the lab figures, but the results were very similar so it is definitely a genuine score.

What does this all prove?

Well, firstly it’s important to state that all of the cars above passed their official government lab tests – even the Subaru and all those Renaults – so there is no question that they are legal. What is shows is how inadequate the regulations are at properly cracking down on emissions levels from diesel cars.

Industry bodies like the SMMT can bleat on about how efficient and environmentally-friendly modern diesel engines are, but the above tests show that it’s largely a charade. So don’t be surprised when governments and councils continue to levy additional taxes on diesel cars, and don’t believe industry representatives who complain that it’s not fair.

Stuart Masson
Stuart Masson
Stuart is the Editorial Director of our suite of sites: The Car Expert, The Van Expert and The Truck Expert. Originally from Australia, Stuart has had a passion for cars and the automotive industry for over thirty years. He spent a decade in automotive retail, and now works tirelessly to help car buyers by providing independent and impartial advice.

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