Tokyo, Japan - Mitsubishi, which acknowledged last week it had intentionally lied about fuel-consumption data for some of its models, said an internal investigation found such tampering dated back to 1991.

President Tetsuro Aikawa told reporters on Tuesday the probe was ongoing, suggesting that more irregularities might be found.

“We don't know the whole picture and we are in the process of trying to determine that,” he said at a news conference at the transport ministry. “I feel a great responsibility.”

Aikawa said so much was unknown that it was uncertain what action the company would take. He said he didn't know why employees resorted to such tactics to make mileage look better.

Mitsubishi had repeatedly promised to come clean after a huge scandal 15 years ago involving a systematic cover-up of auto defects.

The inaccurate mileage tests involved 157,000 of its eK wagon and eK Space light passenger cars, and 468 000 Dayz and Dayz Roox vehicles produced for Nissan.

The models are all so-called “minicars” with tiny engines whose main attraction is generally great fuel-efficiency. They were produced from March 2013. The problem surfaced after Nissan pointed out inconsistencies in data.

Nissan found the company's fuel-consumption goal for the minicars that had been set in 2011 was suddenly raised in 2013. Why that happened is unclear, according to officials.

Aikawa also said it was unclear how customers would be compensated because the extent of the cheating was still under investigation.

Also read: Mitsubishi fuel data scandal widens

Fuel-consumption fraud is a violation of Japan's fuel-efficiency law for cars because buyers are eligible for tax breaks if they buy a vehicle model that returns low fuel consumption. Possible penalties are still unclear due to the uncertainties over the investigation's outcome, according to the transport ministry.

Mitsubishi, which also makes the Outlander SUV and i-MiEV electric car, has arranged for a panel of three lawyers, including a former prosecutor, to further investigate the fuel-consumption scandal from an outsider's point of view, with a report expected within three months.

Production and sales of all affected models have been halted.

Mitsubishi struggled for years to win back consumer trust after an auto defects scandal in the early 2000s over cover-ups of problems such as failing brakes, faulty clutches and fuel tanks prone to falling off dating back to the 1970s. That resulted in more than a million vehicles being recalled retroactively.

The Mitsubishi brand was tarnished seriously when a wheel rolled off a Mitsubishi truck in 2002, killing a woman who was walking down a sidewalk. That truck had not been recalled but parts had been changed on it under free inspections.


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