Japan's Mitsubishi Motors admitted Tuesday it has been using an improper fuel-efficiency testing method for 25 years and did not know how many cars were affected, widening a data-cheating scandal that has plunged it into crisis.
The latest twist will likely fuel speculation that the misconduct stretched to vehicles sold overseas and will send the number affected vehicles soaring from the more than 600,000 already known.
"For the domestic market, we have been using that method since 1991," Mitsubishi Vice President Ryugo Nakao told a Tokyo news briefing.
"But we don't know the number of models" affected in total, he added.
Last week, Mitsubishi admitted unnamed employees rigged tests to make some of its cars seem more fuel-efficient than they were in reality. It said at the time the rigged testing dated back to 2002.
The firm's Tokyo-listed shares have been in freefall since the story broke on Wednesday, losing about half their value and wiping billions of dollars off its market value.
Mitsubishi President Tetsuro Aikawa has acknowledged that the crisis would damage the firm's finances and told Tuesday's briefing: "I can only apologise."
Officials at the news conference said the company did not change its fuel-efficiency testing method when the Japanese government ordered the industry to use an updated system years ago.
So far, the testing has affected vehicles sold in Japan involving four mini-car models, including cars made for rival Nissan.
But Japan's leading Nikkei business daily said Tuesday the firm had been supplying false results on more models than previously reported.
Transport ministry authorities raided the company's office last week, a decade after the automaker was pulled back from the brink of bankruptcy when it was found to have covered up a series of vehicle defects.
On Saturday, the Nikkei said Mitsubishi plans to compensate customers in a bid to limit the fallout from the scandal.
The embarrassing revelations have raised questions about the Japanese carmaker's future, and pointed to a broader problem in the global car industry as regulators probe other automakers' pollution and fuel-efficiency standards.
German carmaker Volkswagen said Friday the massive engine-rigging scandal it is currently engulfed in pushed it into its first annual loss for more than 20 years, and the final total costs are still not calculable.
Also Friday, Germany's Transport Minister, Alexander Dobrindt, said a probe sparked by Volkswagen's emissions-rigging scandal found irregularities at 16 car brands, including Mercedes, France's Renault, Alfa Romeo, Chevrolet, Hyundai, Jaguar and Nissan.