TOKYO -- An emissions test under real driving conditions found that some Japanese diesel cars produced more nitrogen oxide (NOx) than allowed in laboratory testing.
In response to the emissions scandal of German automaker Volkswagen, the transport ministry tested six domestic-brand models on highways and regular roads.
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.
No such excessive emissions were detected on Mazda Motor's CX-5 and 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 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.