The Japanese government on Thursday conducted on-site inspections of two plants of a subsidiary of IHI Corp., a day after the leading engine maker said fuel efficiency data had been falsified for decades.

IHI Power System Co.'s plants in Niigata and Gunma prefectures were inspected, the transport ministry said, after data was found to have been rigged for 4,361 engines.

IHI said data falsification may have taken place since the late 1980s at theNiigata plant and since 2001 at the Gunma factory.

Transport ministry officials enter IHI Power Systems Co.'s plant in Niigata on April 25, 2024, to conduct an inspection. (Kyodo)

"We will sincerely cooperate and respond. We will make efforts to prevent a recurrence, while seeking guidance from our supervisory authority," IHI said in a statement after the inspection by the Ministry of Land, Infrastructure, Transport and Tourism.

Among the affected engines, some were used in Japan Coast Guard patrol vessels and Hokkaido Railway Co. trains, and likely in fishing boats owned by some municipalities, IHI said.

Test data was falsified to show higher fuel economy, IHI said, adding the data had been corrected.

The misconduct came to light after a whistle-blower at the subsidiary reported the wrongdoing in February.

The inspections come as another blow to IHI, which admitted in 2019 to misconduct in the manufacturing of aircraft engine parts and was ordered by the ministry to improve its operations.

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