Shares of Suzuki Motor Corp. slumped after the Japanese automaker said Wednesday it used an improper method for fuel economy testing. This is the latest in the mileage scandal that hit the country’s carmakers when Mitsubishi Motors Corp. admitted to falsifying fuel economy tests in April.

Suzuki said the fuel efficiency and emission tests were different from Japanese regulations and dated back to 2010. The tests were conducted on 16 models sold in the country and about 2.1 million vehicles were affected, the company said, Reuters reported.

“Any wrongdoing, such as manipulation of fuel efficiency data, were not found,” the company said in a statement, cited by Agence France-Presse. “Some discrepancies were found in the automobile emission and fuel-efficiency testing process” between the testing method put forth by the government and what Suzuki did, it added.

Suzuki Chairman Osamu Suzuki will report the issue to Japan’s transport ministry Wednesday, company spokesman Hidehiro Hirano told Bloomberg.

Suzuki's shares closed down 9.4 percent Wednesday, its biggest decline in over seven years. Earlier in the day, the stock had plunged as much as 15 percent. Suzuki’s market value is nearly $11.7 billion, and the stock is down 29 percent this year.

Suzuki’s admission of improper fuel tests comes after Mitsubishi said last month it had falsified fuel economy data on about 625,000 light vehicles. Following the revelation, Japanese transport ministry had ordered all carmakers in the country to show their compliance with government testing methods.