Three days before he lost his job in October, then-Renault SA chief Thierry Bolloré demanded an independent audit of Nissan Motor Co.’s investigation into former Chairman Carlos Ghosn, citing concerns the probe was tainted by conflicts of interest, according to a letter by Mr. Bolloré.

Nissan rejected the demand, accusing Mr. Bolloré of being a Ghosn sympathizer. The boardroom clash pointed to how secret moves by the Japanese car maker’s executives last year that resulted in Mr. Ghosn’s arrest are still disrupting management.

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