The European Union has agreed on tougher emissions tests for diesel cars after the Volkswagen scandal showed previous methods were ineffective.
The new standards give car makers five years to bring them close to what the real emissions standards should be.
The European Commission said that the new tests will more closely resemble real road conditions.
From September 1 2017 new car models will have to pass the new emissions test before they can be put on the market.
EU Commissioner Elzbieta Bienkowska said: "The EU is the first and only region in the world to mandate these robust testing methods."
Until now, car companies had legal ways to cut corners on the emissions tests.
They used a single example of the car model - a so-called "golden vehicle" - that was outfitted especially to do well on the tests. The back seats might be pulled out to reduce weight, for example, or the doors taped over to reduce air drag.
That means that the cars emit far above the technical limits when used on the road - an average of about 400% more.
Under the new deal, the car makers will be allowed to exceed more than twice the agreed emissions limits until September 2017 for new models, and until 2019 for any new vehicles.
The amount by which new models will be allowed to exceed the emissions limits will be reduced to 1.5 times by 2020, and by 2021 for all new vehicles.
Experts from the 28 EU nations approved the methods by a "large majority".
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