Mazda-Emblem_resize An emissions test under real driving conditions found that some Japanese diesel cars produced more nitrogen oxide (NOx) than allowed in laboratory testing.

Japanese diesel cars spewed more emissions on road than in lab

In response to the emissions scandal of German automaker Volkswagen, the Japanese transport ministry tested six domestic-brand models on highways and regular roads. And there’s good news for Mazda owners, Mazda was the “only” brand among 4 Japanese makers to prove its lower NOx emission under the standard in the first road test conducted by Japanese authority in response to the scandal of Volkswagen’s diesel.

In addition, no such excessive emissions were detected on the Mazda CX-5 and Mazda2 (Demio) models. Current law requires only in-lab tests, and the standards are set on that basis, so the four Japanese models do not fail any requirements, the ministry said. But the government is considering new regulations based on road tests, so manufacturers would likely have to respond accordingly.

NOx emissions were measured at two to five times the standard on Toyota Motor’s Land Cruiser Prado and HiAce, Nissan Motor’s X-Trail and Mitsubishi Motors’ Delica D:5. Emissions reached as high as 10 times the standard in part of the driving test. No illegal software was found.

In addition, NOx emissions are said to vary based on factors such as weather and how the vehicle is driven. Discrepancies between in-lab and road tests have been noted repeatedly.