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Mercedes recalls 3 million diesel cars to tackle emissions

Daimler, the parent company of Mercedes-Benz, is to start a voluntary recall of almost every new diesel car bought in the UK over the past six years, in a bid to reduce nitrogen oxide (NOx) output. German company Daimler says that recalled cars will undergo a software update which will reduce NOx emissions, adding that the move will ‘strengthen confidence in diesel technology’. Although inconvenient, the software update will be at no extra cost to owners, according to Daimler.

Mercedes is likely to begin contacting affected owners in the next few weeks. Mercedes is one of the few manufacturers to produce petrol cars that produced a high amount of NOx in Which? tests. In fact, in our tests we found that the Mercedes SL (2012-) produced three times as much NOx as the Euro limit it officially conforms to.

To put that in perspective, it’s the only petrol car we’ve seen that would also fail diesel-equivalent limits. Daimler has yet to confirm exactly how many UK owners will be affected, but has revealed that 1 million vehicles in Germany and 2 million vehicles in the rest of Europe are to be recalled. Diesel cars have been under a lot of scrutiny with recent car emission scandals.

Our in-depth testing uncovers a car’s true emissions, which means we can reveal the dirtiest and cleanest carmakers[1].

Why do car emissions matter?

There’s little doubt about it: air pollution is a threat to the nation’s health. Estimates of fatalities from air population range up to 40,000 deaths per year in the UK, though it’s difficult to determine the precise number. Research shows that high pollution days also tend to coincide with a higher rate of hospital admissions and premature death.

You may think that purchasing a car with a lower MPG (fuel economy) would translate to lower emission levels. Surprisingly, our unique testing has discovered no strong link between a car’s MPG and its emissions. MPG levels may also not be as reliable as you would think, with up to 98% of cars not matching their fuel economy claims.

What’s more, we’ve even found hybrids that produce high levels of toxic emissions. We won’t award a car a Which? Best Buy if it produces a lot of toxic emissions.

Head straight to our latest car reviews[2] to find a model that gives you peace of mind.

Diesel cars that produce the most NOx

Our in-depth tests have found significant differences in emission levels from different brands, despite official limits that carmakers must abide by. Of the cars that comply with official Euro 5 or Euro 6 limits, some car brands – such as Jeep and Dacia – emit far more emissions than other brands in our tests. Our tests show Renault is one of the most polluting carmakers.

NOx emissions from the 16 Renault diesel cars we tested were, on average, nine times higher than the diesel Minis we’ve seen.* Official tests are currently only based on the NEDC cycle which doesn’t strain the vehicle during testing, and is due to be replaced this September. There are also different loopholes that manufacturers can exploit for better readings, such as running the car in eco-mode and over-inflating the tyres.

Our emission tests are based on more realistic conditions to provide more accurate performance levels. This includes the Worldwide-harmonised Light Vehicles Test Procedure (WLPT) cycle that includes running cycles when the engine is both cold and warmed up. We also use a motorway cycle where the vehicle accelerates to and then sustains motorway speeds, a typical scenario for drivers.

Take a look at our guide on cars that produce the most NOx[3] to discover the 10 worst diesel offenders.

*Average NOx emissions for Euro 6 diesel Minis: 0.08.

Average NOx emissions for Euro 6 diesel Renaults: 0.72


  1. ^ the dirtiest and cleanest carmakers (
  2. ^ latest car reviews (
  3. ^ cars that produce the most NOx (

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