Mitsubishi Motors has admitted that since 1991 it had been falsifying fuel economy data, at least in its home market.
Overnight, Japan's sixth largest automaker announced the findings of an internal investigation, six days after it publicly admitted that it had "improperly" provided "better fuel consumption rates" to the Japanese government's Ministry of Land, Infrastructure, Transport and Tourism (MLIT).
Mitsubishi Motors Corporation (MMC) arrived at these improved figures by using a testing method that was "different from the one required by Japanese law".
Above: Mitsubishi eK Space.
At least four kei cars, the Mitsubishi eK Wagon and eK Space, and the badge engineered Nissan Dayz and Dayz Roox, are known to have artificially inflated fuel economy ratings. The four Mitsubishi-produced vehicles, which have been on sale since 2013, have now been withdrawn from sale.
According to the preliminary investigation, in 1991 Mitsubishi began using a "high-speed coasting test" methodology to calculate its fuel economy figures. This was in direct contravention of the newly introduced Road Transport Vehicle act, which required the use of a different coasting test for testing driving resistance.
In 2001, the company compared the official coasting test with Mitsubishi's high-speed version. Mitsubishi says that "the difference in results was found never to exceed 2.3 percent".
Above: Nissan Dayz Roox, produced under contract by Mitsubishi.
Although Mitsubishi updated its internal testing manual in 2007 to specifically state that government mandated TRIAS coasting test should be used for domestic vehicles, the company continued to use its own high-speed coasting test instead.
With the preliminary investigation now complete and submitted to MLIT, the company has vowed to "continue to work to discover the causes of this improper conduct and who is responsible".
To that end, Mitsubishi has established a special investigation committee consisting of lawyers "who have no conflicts of interest with MMC". The three-man committee will be headed up by Keiichi Watanabe, who only recently retired as superintending prosecutor at the Tokyo High Prosecutors Office.
Australia and the rest of the world
As "sufficient investigation has not been made into MMC vehicles other than the [four] mini-cars", the company says that it will issue a "separate report after looking into those models".
Mitsubishi has yet to determine whether cars sold outside of Japan were involved in its fuel economy falsification scheme. At the time of original admission, the company said that it would "conduct an investigation into products manufactured for overseas markets".
Since news of the scandal broke, Mitsubishi Motors' share price has halved from 864 yen ($10.12) to 434 yen ($5.08) at the time of publication.