Japanese automaker Mitsubishi Motors Corp (MMC) on Wednesday, April 20 said it had conducted improper fuel efficiency tests to show better fuel consumption rates in over 600,000 vehicles.

"In connection with the certification process for the mini-cars manufactured by MMC, we found that with respect to the fuel consumption testing data submitted to the Ministry of Land, Infrastructure, Transport and Tourism (MLIT), MMC conducted testing improperly to present better fuel consumption rates than the actual rates," said the company in a press statement.

The company admitted that the misconduct involved four mini-car models — "eK Wagon" and "eK Space" manufactured and sold by MMC, and two others, "Dayz" and "Dayz Roox," manufactured by MMC for Nissan Motors Corporation (NM). MMC said an investigation will also be carried out on the products manufactured for overseas markets.

"We express deep apologies to all of our customers and stakeholders for this issue," said the company, adding that, "the testing method was also different from the one required by Japanese law."

While the company is yet to decide on the compensation, Mitsubishi stated a decision has been taken to stop the production and sales of all the affected models.

Last year, German auto-maker Volkswagen admitted that it had fitted a cheat device in some of its diesel cars to pass emission tests illegally.