Nissan Motor Co.'s latest revelation that improper quality checks performed by unauthorized staff continued at its factories after initial claims it had resolved the issue shows that the car manufacturer has a long way to go to clear up its compliance problems.

Nissan President Hiroto Saikawa told a news conference late Thursday that the final inspection using uncertified staff had been a "norm" at assembly plants, which led to the misconduct continuing even after the company took preventive measures by Sept. 20.

"I am deeply sorry for customers who trusted our preventive measures," Saikawa said at the headquarters of the nation's No. 2 carmaker in Yokohama.