Nissan Motor Co. said Wednesday that improper safety inspections performed by unauthorized staff continued at one of its assembly plants even after the scandal came to light last month.

The carmaker said an internal probe, carried out with a third-party investigator, discovered that at its Shonan factory in the city of Hiratsuka, Kanagawa Prefecture, uncertified staff continued to be involved in a process to check the steering of finished cars until Oct. 11 — a week after Nissan President Hiroto Saikawa publicly apologized for the misconduct. The Shonan factory is operated by Nissan's manufacturing affiliate Nissan Shatai Co.

The uncertified employees were asked to hold and turn the steering wheels of completed vehicles while certified inspectors checked whether the wheels were aligned at the correct angle based on reading of testing equipment.