Police have sent papers to prosecutors on Nissan Motor and three of its employees on suspicion that they had illegally carried out test runs of redesigned passenger cars on public roads, Kyodo News reported.

According to the police, the Nissan employees installed a newly developed engine in two passenger cars in 2003 at the company's factory in Yokosuka, Kanagawa Prefecture, and ran the vehicles on public roads until February this year without registering the renovation in the automobile inspection certificate, in violation of the Road Trucking Vehicle Law.

The two cars ran on public roads in the prefecture for more than 10,000 kilometres [6,000 miles] each, the police told Kyodo News.

The three employees, one of them a 46-year-old in a senior post, reportedly told the police they did not fully understand the law.