Mitsubishi Motors Corp.'s disclosure that it manipulated fuel economy tests risks putting the carmaker back in a familiar position: needing help from Mitsubishi group companies to stay in business.

President Tetsuro Aikawa bowed in apology Wednesday before telling reporters the fuel efficiency of 625,000 minicars had been exaggerated by as much as 10 percent. The firm's shares were set to fall by the 20 percent daily limit Thursday in Tokyo trading after plunging 15 percent Wednesday, the biggest decline in more than a decade.

A bigger issue may lie in store: Mitsubishi Motors has been testing cars using a method not compliant with Japanese standards since 2002, according to Aikawa. While the company said it is unclear whether the flawed method enhanced or reduced fuel economy, further revelations that ratings have been exaggerated may overwhelm the carmaker, which has the lowest level of cash among its Japanese peers. The company required two rounds of bailouts more than a decade ago from Mitsubishi group companies to survive a scandal involving a cover-up of deadly defects.