24 Apr 18

Do you know your Euro 6 from your 6c and 6d-TEMP?

All new cars are Euro 6, but some are more Euro 6 than others. The letters following the number 6 (i.e. b, c or d) are indicative of the fact that they comply with the very latest version of the emission standard or not – and indeed face a possible ban from low-emission zones, or a (more or less) carefree future.

Between Euro 1 (1992) and Euro 6 (2014), emission limits have come down step by step, with different thresholds for petrol and diesel engines being introduced with the arrival of Euro 2 in 1996.

Source: Wikipedia

Since 2014, Euro 6 has been updated - and it will continue to be updated over the next years. Why is the EU calling these updates Euro 6c, 6d-TEMP and 6d rather than continuing counting and name the latter Euro 7, 8 and 9?

The answer lies in dieselgate, or rather: the fact that independent tests revealed dramatic discrepancies between NOx emissions measured in lab conditions – for type-approval purposes – and real-life measurements.

Euro 6c: WLTP

The emission limits set by Euro 6 in 2014 – not only for NOx, but also for particulate matter (PM) and all other toxic emissions – have remained the same, even though there are “updates”, indicated by the letters b, c and d.

These limits are valid for the tests performed in lab conditions in order to type-approve a car. Since September 2017, the tests concerned are carried out on the basis of WLTP rather than the outdated NEDC. That is why Europe changed the name of the standard from Euro 6b to Euro 6c. In other words, the standard hasn't changed, but the measuring method has.

However, along with WLTP came RDE (for Real Driving Emissions), a test carried out on public roads to make sure 'reality' matches 'controlled environment'. It is this RDE that imposes intermediate steps towards a truly new emission standard – indeed, Euro 7, which is likely to come into effect in the mid 2020s.

Euro 6d-TEMP and Euro 6d: RDE

Reality shows that OEMs have a hard time to close the gap between real (RDE) and lab (WLTP), especially in terms of NOx emissions. To cut them some slack, Europe allows a deviation between RDE measurements and WLTP measurements. In a nutshell: Euro 6c is the standard for WLTP measurements, while Euro 6d-TEMP is the one for RDE measurements.

Euro 6c (WLTP, i.e. lab conditions), which took effect on September 1st 2017 for new type approvals and is mandatory for all new cars from September 2018 onwards, means that NOx is limited to 60 and 80 mg/km for petrol and diesel, respectively. Euro 6d-TEMP (RDE, i.e. real driving conditions), which also took effect for new type approvals on September 1st 2017 but gives existing models time until September 2019, allows a deviation (a.k.a conformity factor) of 110 percent.

Indeed, as a temporary measure (hence Euro 6d-TEMP), petrol cars can emit 126 mg/km while tested on the road, diesel cars 168 mg/km. By 2020, when Euro 6d takes effect, the allowed deviation between RDE and WLTP is reduced to 50 percent. Petrol cars must then stay below 90 mg/km, diesel cars are to keep their NOx emissions under 120 mg/km.   

Which cars are already Euro 6d-TEMP?

Basically every new model that has been type-approved since September 2017, plus existing models that have already made the switch ahead of the general introduction of Euro 6d-TEMP in September 2019. You can find a list of these vehicles here.

If you are wondering whether it would be possible to have older Euro 6(b) diesels (from 2014 till today) fixed to make sure they comply with Euro 6d-temp: the answer is quite complicated.

It is believed that software changes alone won't to the job, but Germany's chancelor Merkel has reservations about forcing carmakers to introduce hardware modifications, such as changing filters in exhaust systems. “The benefits and costs must be proportionate. Hardware refits are relatively cost-intensive,” said Merkel.

Automotive researcher Mark Pecqueur disagrees: he believes €1,000 per car should suffice to fix the NOx problem.

WLTP, NEDC correlated, RDE in a nutshell

Things are indeed complicated, but our video "WLTP: 7 questions and 7 answers" and "WLTP, NEDC, NEDC correlated, RDE: what's it all about" explain what to expect and how it impacts company car drivers, fleet managers, OEMs and leasing companies.

In case you were wondering whether real-world NOx emissions are really lower since the introduction of Euro 6d-temp: recent data shows that NOx emissions on the road have been reduced by 99 per cent.

Keep calm and diesel on?

That's a very good question. Click here to read our analysis.

Picture copyright: TÜV Nord, 2018

Authored by: Dieter Quartier