TOKYO (BLOOMBERG) - Shares of Suzuki Motor plunged after saying it found an improper method used to test the fuel efficiency of its vehicles, widening a scandal for Japan's auto industry that first originated with Mitsubishi Motors.

Chairman Osamu Suzuki will report the issue to Japan's transport ministry on Wednesday ( May 18), spokesman Hidehiro Hirano said by phone. The company hasn't found a flaw affecting the fuel efficiency of Suzuki vehicles, he said, without elaborating.

Suzuki slumped 15 per cent to 2450.5 yen as of 12.55 p.m. in Tokyo trading. The company has a market value of about US$11 billion, and the stock is down 33 per cent this year.

Japan's transport ministry had asked automakers to investigate their handling of fuel economy tests in the wake of Mitsubishi Motors' disclosures that it overstated the ratings of four minicar models by as much as 10 per cent. Mitsubishi Motors has said it manipulated data related to those cars and has been investigating use of improper testing of other models dating back to 1991.

Mitsubishi Motors president Tetsuro Aikawa has decided to leave the automaker because of its scandal, the Nikkei reported earlier on Wednesday, without saying where it got the information. Suzuki, 86, ceded the role of president to his son Toshihiro, 57, in June 2015 after leading the company for 37 years.

Kyodo reported earlier on Wednesday that Suzuki may have improperly tested for fuel economy and would meet with Japan's transport ministry.