Toyota called the breach of compliance principles a "grave issue" and said it is working to identify which of its vehicles might be affected. It said Kobe Steel materials have been used in hoods, rear doors and peripheral areas. The materials were supplied to plants in Japan and factories elsewhere were not affected, Toyota said.
Nissan said it is rushing to check performance because the material is used in parts such as hoods and may affect protection of pedestrians.
Honda said it used the materials in question for doors and hoods of its cars.
Mazda, Mitsubishi Motors, Suzuki and Subaru said they were checking to see which of their vehicles used Kobe Steel products and if there is an impact on safety.