According to a report by Nikkei Asian Review, three Japanese automakers have been discovered to conduct improper fuel economy and emissions tests on their vehicles in the country.

Japan’s Ministry of Land, Infrastructure and Transport (MLIT), confirmed the matter after requesting the three companies to submit reports on the findings prior. Earlier this year, Nissan and Subaru admitted to improper testing conduct, prompting the ministry to probe into other automakers.

Based on random sampling of manufactured vehicles during the quality assurance process, a number of cars were found to have been tested under incorrect driving conditions.

In terms of numbers, Suzuki discovered improper tests on 6,401 out of 12,819 units since 2012. Mazda singled out 72 vehicles out of 1,875 for improper testing since 2014, while Yamaha discovered seven affected units out of 335 since 2016.

Mazda has issued a statement in response to the matter; saying that the investigation confirmed that there has been “no improper alteration or falsification of test data in either mode (JC08 and WLTC).”

Instead, test data showed speed trace errors involving 72 out of the 1,472 vehicles tested under the JC08 mode. A speed trace error is a situation in which a vehicle’s speed deviates more than the permitted amount from the speed trace pattern prescribed by the test mode.

At a press conference, Kiyotaka Shobuda, Mazda’s senior managing executive officer, told reporters that there were no deliberate alterations to the data, and that the quality of the cars weren’t compromised because of improper testing. He added that the company will make sure to prevent improper inspections in the future.

Meanwhile, Suzuki president Toshihiro Suzuki apologised for his company’s actions, saying, “it is a significant fact that such a large number of our products were improperly processed, and we take it seriously. We failed to educate our staff in an in-depth and extensive manner.”