On Friday Japan’s Ministry of Transportation said that it had found discrepancies between lab and real-world emissions measurements for diesel vehicles from Toyota, Nissan, and Mitsubishi. However, the ministry said that it had not found any illegal software on the vehicles and that the automakers had not violated any of Japan’s regulations.

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According to the Wall Street Journal , Toyota’s Hiace van and the Land Cruiser Prado sport-utility vehicle, as well as Nissan’s X-Trail SUV and Mitsubishi’s Delica D:5 all emitted between four and 10 times the amount of nitrogen oxide (NO) that is allowed in Japan's real-world driving tests.

Japan has been testing vehicles sold in the country after the US Environmental Protection Agency (EPA) discovered that diesel vehicles sold by Volkswagen Group were emitting many times the legal limit of NO x due to illegal software placed on the cars that let them cheat on lab testing conducted by regulators. The ensuing scandal has sent Volkswagen’s stock into a nosedive and has potentially put the company on the hook for tens of billions of dollars in fines.

Japanese regulators told the WSJ that tests of Mazda’s CX-5 and its Demio (internationally known as the Mazda2) resulted in lab and real-world tests that were almost exactly the same.

Japan has offered tax breaks for people who buy diesel cars, which are promoted as greener and more eco-friendly than gasoline-powered cars.

Currently, the WSJ says, diesel vehicles must pass a 20-minute lab test before they can be sold in Japan, but Japan Times reports that the Ministry of Transportation has decided to make road tests standard for diesel vehicles before they can be sold there. France also took similar steps earlier this year to do on-road tests of vehicles. Regulators there found that a Renault model had higher-than-permitted emissions.

Officials attributed the discrepancies found in the tests of Toyota, Mitsubishi, and Nissan’s vehicles to a function of the cars that shuts off the exhaust gas recirculation system in cold weather, thereby leading to increased NO x emissions.

The three companies gave statements to the WSJ saying that they would continue to follow regulations and make efforts to reduce on-road emissions. Japan Times notes that the increased scrutiny from regulators "could raise concerns among carmakers over the image of diesel cars and the potential higher development costs to keep emissions legal."