Nissan Motor Co. said Monday that it found its employees had fabricated data and conducted irregular tests in inspecting new vehicles at five domestic plants, the latest setback for a company embroiled in an inspection scandal last year.

The Japanese automaker said data from emissions or fuel efficiency tests had been falsified between April 2013 and June this year. Also some tests were conducted at room temperatures, humidity levels and other conditions deviating from those required.

Nissan said 10 workers at the plants were involved in the misconduct that affect 1,171 vehicles of 19 models or 53.5 percent of the total vehicles tested during the period. The company carries out these tests on 1 percent of the vehicles produced.

Nissan was found last year to have allowed uncertified employees to inspect vehicles for many years, leading the company to recall over 1 million vehicles sold within Japan.

(Nissan Chief Competitive Officer Yasuhiro Yamauchi, right, bows in apology.)

"We sincerely apologize to our customers as we found such misconduct at a time when we are working on preventive measures" to address last year's inspection failings, Yasuhiro Yamauchi, Nissan's chief competitive officer, said at a news conference at the company's headquarters in Yokohama.

Nissan said it plans to recall none of the affected vehicle as the latest improper tests have no impact on vehicle safety.

The revelation follows similar scandals at plants of Subaru Corp. which said last month that it found more cases of product data fabrication. Subaru's president stepped down to take responsibility for the inspection scandal.

The Ministry of Land, Infrastructure, Transport and Tourism directed Nissan to report preventive measures for the latest data tempering in one month.