Japanese car manufacturer Mitsubishi Motors has admitted conducting testing ‘improperly’ to present better fuel consumption than the actual rates of some of its mini-cars to the Japanese Ministry of Land, Infrastructure, Transport and Tourism.

The manufacturer also said that the testing method used for the mini-cars was different from the one required by Japanese law.

The mishandled fuel economy tests, apart from being applicable to Mitsubishi ‘eK Wagon’ and ‘eK Space’ models, affected ‘Dayz’ and ‘Dayz Roox’ models, which have been manufactured by Mitsubishi and supplied to Nissan Motors Corporation since June 2013.

Since Mitsubishi developed the applicable cars, it was responsible for obtaining the relevant certifications and conducting fuel consumption testing.

In the process of developing next-generation mini-car products, Nissan examined the fuel consumption rates of the applicable cars for its ‘reference’ and found deviations in the figures. Nissan requested Mitsubishi to review the running resistance value set by Mitsubishi driving tests.

"In the course of our internal investigation upon this request, MMC [Mitsubishi] learned of the improper conduct that MMC used the running resistance value for testing which provided more advantageous fuel consumption rates than the actual rates," wrote Mitsubishi.

Mitsubishi and Nissan have decided to stop production and sale of the applicable cars.

Up until the end of March 2016, Mitsubishi sold 157,000 units of the eK Wagon and eK Space and supplied 468,000 units of the Dayz and Dayz Roox to Nissan.

A press release by Mitsubishi said that the company will discuss with Nissan about compensation regarding this issue.

Nissan and Mitsubishi established a joint venture in NMKV in June 2011 to specialize in the planning and development of minicars. Last October, the companies and their joint venture reached an agreement to continue their joint project an unveiled the planning and development of a minicar EV.

Mitsubishi announced that it will also conduct an investigation into products manufactured for overseas markets.