Kobe Steel Ltd said on Wednesday it has found cases of data falsification in its iron powder products and at its research unit.
On Wednesday fresh revelations showed data fabrication at the steelmaker was more widespread than it initially said, as the company joins a list of Japanese manufacturers that have admitted to similar misconduct in recent years.
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.
Investors have also rushed to unload Kobe Steel's bonds, causing the extra yield demanded to hold the securities over Japanese government notes to jump.
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Hitachi said its new trains in Britain used Kobe Steel but had all passed rigorous tests.
Honda spokesman Tamon Kusakabe told AFP: "As to safety, we are still studying (a possible) impact".
Auto giant Toyota has already said Kobe Steel supplied materials to one of its Japanese factories, which used them in hoods, rear doors and surrounding areas of certain vehicles. "At the same time, we are considering what measures need to be put in place going forward".
About 200 of Kobe Steel's customers, including some makers of defence equipment, were affected, Nogami said.
Boeing said in a statement it was working "with our suppliers since being notified of the issue".
It was unclear if the total of 40,900 tons of products involved included shipments to other countries.
Analysts say the announcement further tarnishes the reputation of Japan's globe-trotting manufacturers, long celebrated for their high-quality products.
"Nothing in our review to date leads us to conclude that this issue presents a safety concern", it said.
They include cases of falsified data at Nissan Motor and Mitsubishi Motors, while air bag maker Takata filed for bankruptcy in June over faulty airbags which were blamed for several deaths and many injuries.
Hiroya Kawasaki told reporters the cheating scandal has left Kobe Steel's credibility at "zero", underscoring the deepening crisis at the steelmaker and the sweep of quality problems besetting Japan's once-vaunted manufacturing sector.