Let’s start with laying down some basic facts regarding Euro-6 regulation, to avoid any confusion. All new cars (including petrols, diesels and hybrids, but not pure electric cars!) manufactured since September 2014 have been required to be Euro-6 compliant… but in reality, some are more Euro-6 compliant than others, as we will now explain!

After the basic identification “Euro-6” are appendages, such as a, b, c, or d, and other codes like TEMP, that are mostly indications of progressive test methods development from the original Euro-6 tests. With the exception of RDE testing (more on that later), the various limits have remained unchanged. So, as the tests have changed, these new identifiers indicate whether the car in question complies with the latest test procedures and methodology. These variations from the base 2014 Euro-6 regulations might possibly in future determine the treatment of any car in low-emission zones, although to date there is no sign yet of any such retrospective legislation. With so many earlier and much dirtier Euro-4 and -5 cars still on the road, to introduce any such restrictions would, we feel, be quite unworkable and confusing.

This further development of the initial Euro-6 regulations by changes in the test procedures was arguably one of the beneficial outcomes of the “Dieselgate” scandal. The new procedures were developed to address the revelations that existing NEDC (New European Driving Cycle) laboratory emissions testing was fundamentally flawed (this had already been known for some years!) and that these tests needed changing, and further supplemented with realistic on-road emissions testing for RDE, or real driving emissions, primarily with NO_x emissions regulation in mind.

So what precisely do these letters after the number 6 mean? Euro-6a was an approval code given to cars submitted voluntarily for early Euro-6 approval, when Euro-5 limits were still acceptable, and Euro-6b was that used to identify a three-year concession for petrol cars allowing higher particulate emission limits – so enough said about that! The first really significant change came with Euro-6c, which indicated the switch from the old NEDC laboratory test cycles to more realistic WLTP (Worldwide Harmonised Light Vehicle Test Procedure) testing. This was then followed by Euro-6d (sometimes called Euro-6d RDE) with the introduction of RDE, the on-road testing procedures. This has commenced with provisional limits set higher than the tougher full RDE targets, which were effectively postponed, giving manufacturers time to develop the necessary improvements. To indicate this, the word TEMP was added, indicating that the RDE NO_x test limits were temporarily set at these higher levels, until September 2020, when the NO_x limits will be reduced by 28.5 per cent. You can have a pure Euro-6d badge for your car though, if it can pass those tighter NO_x RDE limits now, and some indeed have, including those from BMW, Jaguar, Land Rover and Mercedes-Benz.

Finally, we have seen the recent the introduction of Euro-6d TEMP EVAP ISC, as if things were complicated enough! The EU has introduced these further amendments to the Euro-6d-Temp emission standard (and Euro-6d in due course) requiring that OEMs (Original Equipment Manufacturers) measure evaporative emissions from the car’s fuel tank (EVAP) over 48 hours. These will generally affect petrol cars, not diesel, though. The ISC approval will be required to verify that the actual emissions of cars are maintained when they are in service (In Service Conformity) over five years, or 100,000kms. Serious doubts have been expressed as to when its enforcement will be practicable, since we already know from past involvement that the facilities for testing significant numbers of randomly selected cars drawn from the UK car fleet are near to non-existent.

That’s it in a nutshell, and hopefully this clarifies things for Diesel Car & Eco Car readers. We can dispel any hopes that, by leaving the EU, the UK might escape such fun, since it is almost inevitable that, even outside of the EU, the UK will remain committed to the EU regulatory emissions control system.