Mazda Motor Corp, Suzuki Motor Corp and Yamaha Motor Co conducted improper fuel economy and emissions tests on their vehicles, Japan’s transport ministry has said.
The findings were the results of internal investigations ordered at Japanese car makers after improper testing at Subaru and Nissan.
Representatives for Mazda and Suzuki confirmed they submitted reports regarding improper testing. Yamaha Motor confirmed it carried out inappropriate testing.
Mazda shares fell to their lowest in nearly four weeks. Suzuki shares were down as much as 5.2 percent, with Yamaha shares were down 4 percent.
Suzuki, Japan's fourth-largest car manufacturer, said that of 12,819 sample cars tested for fuel economy and emissions since June 2012, around 50 percent had been inspected improperly.
"I deeply apologise and will lead efforts to prevent recurrence," CEO Toshihiro Suzuki told a news conference.
In July this year, Nissan admitted it had improperly measured exhaust emissions and fuel economy for 19 vehicle models sold in Japan.