Baku, April 20, AZERTAC
Mitsubishi Motors has admitted falsifying fuel economy data for more than 600,000 vehicles sold in Japan, according to BBC.
Tyre pressure figures were falsified by employees to flatter mileage rates, the company said.
Almost 470,000 vehicles that Mitsubishi made for Nissan were affected and the issue was uncovered after Nissan found inconsistencies.
The announcement sent shares in Mitsubishi down more than 15% in Tokyo.
Company bosses, including Mitsubishi Motors president Tetsuro Aikawa, bowed deeply at the start of a press conference on Wednesday afternoon in Tokyo.
The inaccurate tests involved 157,000 of its own cars and 468,000 vehicles produced for Nissan.
The issue affected models including Mitsubishi's ek Wagon and eK Space, as well as Nissan's Dayz and Dayz Roox.
All are "mini-cars" with 660cc petrol engines and are popular in Japan but have found little success in other markets.
Lance Bradley, UK managing director of Mitsubishi Motors, said there was no evidence that any models sold in the UK or Europe were affected.
The company is Japan's sixth-largest car maker and sold more than one million vehicles last year, but has less than 1% of the UK market.