A major affiliate of Japan's Toyota Motor Corp falsified emissions data on some engines as far back as 2003, more than a decade earlier than previously indicated, a company-sponsored probe showed on Tuesday.

The investigative committee tasked by automaker Hino Motors Ltd blamed the scandal on an environment where engineers did not feel able to challenge superiors, in a rare criticism of corporate culture in Japan.

The committee, composed of lawyers and a corporate adviser, was set up by Hino this year after it admitted to falsifying data related to emissions and fuel performance of four engines. Its findings, released on Tuesday, detail an inflexible atmosphere where it was difficult for staff to feel "psychological safety", the committee said in a report.