/ Motoring

What’s the truth behind car emissions claims?

Come clean on fuel claims

Our testing has found that almost all modern diesel cars exceed official emissions limits when tested in real-world conditions. We even found some hybrids breaking the limits too. So how can we trust car emissions claims?

Consumer news in 2015 didn’t get much bigger than the Volkswagen (VW) emissions scandal. The ramifications were (and still are) huge – not just for VW and the owners of affected cars, but for the whole motor industry.

Our testing is different to the official testing procedure used. It still takes place in a lab, but we use more challenging and realistic driving cycles to provide more accurate figures.

So using our lab results on over 300 cars that we’ve tested since 2012, we did a deep dive on the data. And the results were interesting.

It’s not just VW – and not just diesels either

What we found is that it’s not just VW that have been pumping out some peculiar claims. We looked back over three years’ worth of data, across all manufacturers whose cars officially comply with modern emissions regulations, known as Euro 5 or Euro 6 depending on the age of the car.

What we found was an astonishing 95% of diesel cars exceeded oxides of nitrogen (NOx) limits in our testing. The worst offender emitted 15 times more NOx as its Euro 5 engine is permitted to.

And it’s not just diesel engined cars either. We found that one in ten petrol cars produced so much NOx that they too are breaking emission limits. Now, petrol cars do also produce NOx, but this is supposed to be in such small quantities that it’s of little significance and well under the limits set. The worst offender we found emitted 15 times more NOx as its Euro 5 engine is permitted to.

Carbon monoxide

We also found two thirds of petrol cars are creating far more carbon monoxide (CO) in our tests than EU limits.

CO is different to carbon dioxide (CO2) – CO2 is harmful to the environment and your car tax is based on how much CO2 your car creates. CO on the other hand is much more harmful to human health and has no effect on car tax.

Worryingly, in our tests, two thirds of petrol cars put out more CO into the air than they’re allowed to. The worst created more than five times the amount of CO than the official limit. And it’s not just sporty or big cars that are to blame – several superminis with small capacity engines are among the top offenders. And some were so bad that they couldn’t even meet the early ‘Euro 1’ limits from 1993 – which are pretty lenient compared to modern standards.

To our surprise we also found some hybrid cars are also breaking emission laws. Testing revealed that some petrol-hybrid cars emit more CO than they’re allowed – in fact one petrol-hybrid was the 11th highest CO emitter we’ve found so far.

We’ve also identified a diesel-hybrid that produces more NOx than limits allow. And what makes this even worse is that there is no special lower limits that hybrids are held account to.

So what now?

We want you to be able to trust car makers’ fuel emission and efficiency claims. We need a stringent, independently audited test regime in the EU. It’s no coincidence that the VW scandal broke in the US, where such a test regime operates. The flawed European system allows carmakers to declare lab figures that rarely bear any relation to real-life emissions.

As a VW owner I’m currently awaiting the ‘fix’ to my car, as I’m sure thousands of you are. Last week we heard that VW has no plans to compensate VW owners in the UK, as they have in the US. But I’m curious to know whether this fix it will have any bearing on how my car performs, or on the pollution it produces in daily driving. VW has insisted that there will be no change to performance, but I’ll wait and see.

Since September, more than 78,000 people have backed our ‘Come Clean on Fuel Claims’ campaign. If you agree that more needs to be done to make car manufacturers come clean on emissions claims then back our campaign today. Also, tell us what you think about your car in our Car Survey.

So what do you think about these car emissions claims? Have you been affected at all?

*All Euro dates refer to new car registrations

phantom41 says:
25 January 2016

Pompous Which? says 95% of diesels do not meet standards and yet only list 5 as having been withdrawn from their “Best Buys” list and then – shock horror – go on to de-list 23 from the VW Group – Yah Boo. I agree with many of the previous comments about how Which? tests and their awards. Get a grip Which? list all cars that do not meet the standard. If targets have been set too high then realistic targets should be set and enforced. I am perfectly happy with my VW and have had many VW’s in the past and I certainly do not want any cars dumbed down to meet ridiculous unachievable targets. No, I do not expect compensation nor do I want it. In any case my VW is petrol and I shall never buy a smelly smokey diesel.

John says:
24 March 2017

There is a lot of two-faced opinion being put out there, which clouds the issue (pun … sorry!). The simple fact is that diesel emissions have always been toxic to us all, and continue to be so. I am delighted to see your comment about diesel; I have never had, nor ever will have, a vehicle that produces emissions that are immediately dangerous to health. As regards petrol emissions, CO2 does indeed impact on the environment but, unless one sucks on a tailpipe, will not cause such immediate and direct injury. CO, however, is poisonous but is considerably less so than the NOx gases and particulates from diesel.

VW, which produces many excellent vehicles was, nonetheless, rightly taken to task over the so-called “emissions scandal”, but no-one will ever convince me that ALL the other major manufacturers were (are) not guilty of similar actions. Only in America could the prevailing litigious attitude result in mammoth compensation claims, naturally including massive income for the legal profession. There are apparently “dumps” of diesel vehicles that have been bought back and will, no doubt, eventually be scrapped. I applaud the removal of these vehicles from the roads, even though the motive behind it was NOT on health grounds.


Some European words about emissions testing.


Thanks Malcolm,,,,,,,,,,,,,That made a bit of welcome reading…………According to where one stands of course


In an earlier comment “I expect the EC to coordinate emissions limits and testing programmes………….” They do, as far as I can see, look at atmospheric pollution in the round. A search on the EC’s website might uncover the sort of information required.
For example:
http://ec.europa.eu/unitedkingdom/press/frontpage/2014/14_12_en.htm begins
“Legal proceedings have been launched against the UK for its failure to cut excessive levels of nitrogen dioxide, the Commission announced today. The toxic gas is the main pre-cursor for ground-level ozone causing major respiratory problems and leading to premature death. Most nitrogen dioxide originates in traffic fumes so city dwellers face the biggest exposure.”
and goes on
“The areas affected are: Greater London, West Midlands, Greater Manchester, West Yorkshire, Teesside, the Potteries, Hull, Southampton, Glasgow, East, South East, East Midlands, Merseyside, Yorkshire & Humberside, West Midlands and the North East.

European legislation sets limits on air pollution and the NOx limits should have been achieved by 1 January 2010. However, the EU rules offer some flexibility and extensions have been agreed with Member States who presented a credible and workable plan for meeting air quality standards within five years of the original deadline, ie by January 2015.

The UK has not presented any such plan for the zones in question.”

Later on : “In a separate move, the Commission has also asked Belgium to act on air pollution over its failure to protect the health of its citizens from fine dust (PM10) pollution. In particular, those living and working in Brussels, Ghent port zone, Antwerp (including the port zone), Flanders and Liege have been exposed to unhealthy levels of PM 10 since 2005.”

These pollution levels will not be met just by cleaner cars – other EU countries have the same vehicles but are not mentioned here. Perhaps they are all suffering pollution, or perhaps some have better strategies than the UK?

Cutting vehicle use in towns would reduce pollution substantially. But could we stomach that sort of restriction of “personal freedom” (freedom to poison others, you might think?).


There is no need either to relax emission levels (NOx, CO, particulates, HCs) nor to accept worsened CO2 output, or performance, or fuel economy. The need for emission relaxation is a story weaved by the European motor industry to protect their sunk investment in diesel and in after-combustion treatment accessories.

My company has produced prototypes of a novel type of cylinder head which has been independently tested, academically peer-reviewed, supported by UK Tech Strategy Board funding, and patented. It delivers the best of both petrol and diesel, and beats both on economy and emissions. Not magic, just textbook thermodynamics and a revolutionary new approach to mixing and separating air and fuel flows. Incidentally, it requires no moving parts and needs only one camshaft, not two. So it is cheap to build and maintain.

Despite valiant efforts to engage UK and German car producers, we are now talking to Indian and Korean manufacturers with a view to them developing road-going demonstrators. Not sure why manufacturers closer to home are not willing even to assess the technology.



A look at their website shows bench testing on a single cylinder version between 2000-2004 at Coventry, at Cosworth 1995-96 (which suggests building a 4 cylinder prototype for comparison with existing engines) and at Tickford in 2008 on a 2.0 litre 4 cylinder that failed during test due to a flaw in the cylinder head casting.

Seems to have been going on for a long time if the performance is as promising as given. Surely if there was full confidence in the outcome making a sound cylinder head to demonstrate its real performance would not be an obstacle.

Lets hope they attract the investors needed to decide its worth.


A truly silly report. What next…’Shocking truth that home fuel usage goes up as you raise your thermostat levels’. How can a fuel ecomony and emission test be developed for everybodies different driving styles? ….it can’t. Very poor journalism which I wouldn’t expect from Which.