Mitsubishi Motors Corp. falsified data on mileage tests on light vehicles, the Japanese automaker said Tuesday. Improper tests were conducted on about 625,000 vehicles to improve fuel-economy claims.

The vehicle models that were affected include those supplied to Nissan Motor Co., which uncovered discrepancy in data, Mitsubishi said, in a statement.

“We have decided to stop production and sales of the applicable cars. NM [Nissan Motor] also has stopped sales of the applicable cars, and MMC [Mitsubishi Motors] and NM will discuss compensation regarding this issue,” Mitsubishi said.

“During our internal investigation, we have found that the testing method which was different from the one required by Japanese law has been applied to other models manufactured by MMC for the Japanese domestic market,” the company added.

Shares in Mitsubishi Motors tumbled more than 15 percent in Tokyo Wednesday, which is reportedly the stock’s biggest one-day drop in almost 12 years. The automaker’s market cap reduced by $1.2 billion Wednesday.

Mitsubishi is suspected of influencing the load placed on the tires of its four different models to improve their fuel economy performance claims, a source told Kyodo News, according to Bloomberg.

This is the first time a Japanese automaker has been in involved in manipulating fuel-economy tests. German carmaker Volkswagen was last year found to have cheated in diesel emissions tests in the United States and other countries.