Kobe Steel Ltd said on Wednesday it has found cases of data falsification in its iron powder products and at its research unit.
The industry ministry has pressed Kobe Steel to work with its clients, spread over a wide range of industries, to conduct urgent safety analysis.
The Kobe Steel scandal broke on Sunday when the manufacturer admitted to falsifying data linked to the strength and quality of products.
"Putting the utmost priority on the safety of our customers, we are rapidly working to identify which vehicle models might be subject to this situation and what components were used, as well as what effect there might be on individual vehicles", Toyota said in a statement. The company's shares steadied after a two-day rout.
Shares in Kobe Steel fell by almost 40% in two days, wiping more than $1.5bn (£1.1bn) off its market value after the firm admitted fabricating data about the strength and durability of products it delivered to more than 200 companies.
Kobe Steel plunged deeper into crisis yesterday as fresh revelations showed data fabrication at the steelmaker was more widespread than initially thought. Central Japan Railway said while some Kobe Steel parts for its bullet trains did not meet Japanese industrial standards, there were no safety issues.
Toshiba is still working to recover from an accounting scandal that began in 2015.
The corrosive business practices have raised broader questions over corporate governance in Japan, and cast doubt on the integrity of a manufacturing industry once the envy of the world.
MHI said Kobe Steel products were used on its Mitsubishi Regional Jet and rockets, including a H-2A rocket launched on Tuesday to put a navigation satellite into orbit. The government has urged Kobe Steel to clarify the extent of the misconduct.
However, it declined comment on a media report that materials used in semiconductors were also impacted by the scandal.
Toyota, Nissan, Honda, Mitsubishi Motor, Subaru and Mazda joined aviation firms and defence contractors Mitsubishi Heavy Industries, Kawasaki Heavy Industries and IHI that have used the steel maker's products. Kobe Steel said it had failed to carry out tests it had agreed to conduct, and improperly "rewrote" inspection data.
In a statement on Wednesday, Kobe Steel denied a Nikkei business daily report that it meant to put its real estate business up for sale to help shore up its finances.
The steelmaker reported losses in the last two financial years, but has said it expects to return to profit this year.