Mazda Motor Corp, Suzuki Motor Corp and Yamaha Motor Co improperly tested vehicles for fuel economy and emissions, the Japanese government said on Thursday, revealing fresh cases of compliance failures by manufacturers.
All three have already complied with a request by the Japanese Ministry of Land, Infrastructure, Transport and Tourism (MLIT) to conduct investigations into the matter.
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.
Reuters, meanwhile, reported that Suzuki most often inspected vehicles with manipulated emissions data, adding that the company confirmed that nearly half of its 12,819 new auto inspections were improper dating back to 2012.
The admissions are the latest in a string of scandals involving data falsification and testing standard breaches in Japan's key auto sector.
Mazda said it 72 vehicles or 3.8 percent of those in its sample were affected, while Yamaha put the figure at 2.1 percent of its motorbike sample.
The automakers examined tests they had conducted over different periods of time and in Suzuki's case they stretched back to 2012. Yamaha Motor confirmed it carried out inappropriate testing.
At Mazda, of 1,875 cars subject to the sampling inspection, improper inspections were discovered in almost 4 percent since November 2014.
Results at Japanese affiliates of three foreign automakers - Audi AG, Volkswagen AG and Volvo Cars - were pending, while no irregularities were reported by the remaining 17 companies, the ministry said.
Suzuki and Yamaha shares fell 6 and 5 percent, respectively, and Mazda shares were down 1 percent, underperforming a steady benchmark Nikkei average.
In July this year, Nissan admitted it had improperly measured exhaust emissions and fuel economy for 19 vehicle models sold in Japan.