Nidec Corp shares fell up to 18% to ¥2,329 after confirming suspected quality‑inspection misconduct in certain products.
The company said the issues involve unauthorised changes to materials, processes and designs but do not immediately affect product safety.
Nidec is also dealing with a 160.7 billion‑yen net‑profit hit from accounting revisions covering 2020‑2025.
Nikkei Asia reported over 1,000 cases of quality tampering, prompting Nidec to consider forming an investigation committee.