Analyzes results of emissions tests on 32 Euro 6 diesel passenger cars from 10 different manufacturers. Results show some automakers meeting diesel NOx emissions standards under more realistic driving conditions, while others lag badly. Controlling nitrogen oxide (NOx) emissions from Euro 6 diesel passenger cars is one of the biggest technical challenges facing automakers. Euro 6 limits NOx emissions from diesel passenger cars to 80 mg per kilometer, down from 180 mg/km for Euro 5 vehicles. The new limit value is not as stringent as it appears, because it applies to an outdated emissions certification driving cycle (the New Europea Driving Cycle, NEDC) that should be replaced by a more realistic one (the Worldwide Harmonized Light Vehicles Test Cycle, WLTC) from 2017 on. But the biggest challenge for diesel passenger car manufacturers arises not from the certification cycle but from the real-driving emissions (RDE) test, which is scheduled to become a mandatory step for the type approval of passenger cars in the EU in January 2016. Under this new testing framework, diesel passenger cars will have to prove that they can keep NOX emissions at reasonably low levels during a test that more closely represents real-world driving situations.