For the second time in about a decade, Mitsubishi Motors Corp. faces a scandal that poses an existential threat.

The automaker has improperly tested the fuel economy of its cars for the past quarter century, widening the scope of misconduct that executives initially said dated back to 2002. The Mitsubishi Motors board formed a panel of three ex-prosecutors to investigate for about three months. Until then, customers, investors and minicar partner Nissan Motor Co. may be left waiting for information about the number of affected models and details of compensation.

"I'm taking this as a case that could affect our company's existence," President Tetsuro Aikawa told reporters during a news conference Tuesday. "My mission is to solve the issue."