Suzuki Motor Corp., Mazda Motor Corp. and Yamaha Motor Co. conducted improper fuel-efficiency and emissions tests on their vehicles, the transport ministry said Thursday.

The report is the latest episode in a growing list of data falsifications that have tarnished the image of Japan’s manufacturing industry, known for its high-quality and efficient production.

The findings were the result of internal investigations ordered at the automakers by the ministry after improper testing was found at Subaru Corp. and Nissan Motor Co.

According to the report, Suzuki, Mazda and Yamaha cleared vehicles for emissions or fuel efficiency standards even in cases where they were tested improperly, the ministry said. The ministry looked at tests conducted over different periods at all three automakers. In Suzuki’s case, the time period stretched back to 2012.

Suzuki, Japan’s fourth-largest automaker, said out of 12,819 cars sampled for fuel economy and emissions since June 2012, around half had been inspected improperly.

“I deeply apologize and will lead efforts to prevent a recurrence,” Chief Executive Toshihiro Suzuki told a news conference.

The company, however, said it did not find any significant problems with actual vehicle emissions and fuel efficiency and therefore did not plan to issue any recalls.

A total of 30 models, including those whose no longer being produced, were subject to the investigation. Officials at Suzuki said insufficient training and the absence of supervision by senior workers led to the lax inspections.

At Mazda, of 1,875 cars subject to the sampling inspection, improper inspections were discovered in nearly 4 percent since November 2014. For Yamaha Motor, around 2 percent of 335 units chosen for the sampling inspection had not gone through appropriate testing since January 2016, according to the ministry.

Suzuki, Mazda and Yamaha said they would take preventive steps, such as changing inspection devices so their staff cannot rewrite the data. The ministry said it will instruct them to save records of the inspections and implement measures to detect or prevent data falsification.

Yamaha also confirmed it carried out inappropriate testing and apologized.

The ministry made the results public based on reports from 20 automakers collected as of Wednesday.

“It is extremely regrettable. The ministry will strictly instruct the carmakers to make sure thorough preventive measures are taken,” transport minister Keiichi Ishii said in a released statement.

The quality-control data falsifications have embroiled Kobe Steel Ltd. and Mitsubishi Materials Corp.