Mitsubishi Motors admitted Wednesday that employees submitted false fuel consumption data for four "mini-car" models to Japanese authorities.
The company said that fuel economy tests for the eK Wagon, eK Space, Dayz and Dayz Roox varied from the tests required under Japanese law and that the evaluations themselves were conducted improperly.
The scandal is Mitsubishi's largest since a cover-up of decades of safety issues came to light in the early 2000s.
"We express deep apologies to all of our customers and stakeholders for this issue," the company said in a statement.
Mitsubishi sold about 157,000 eK Wagons and eK Spaces — mini-car models developed with smaller engines for greater fuel efficiency — and supplied another 468,000 Dayz and Dayz Roox models to fellow Japanese automaker Nissan.
Nissan found variations with Mitsubishi's numbers in its own testing and requested a review of the initial statistics.
The subsequent internal probe found that Mitsubishi employees manipulated tire resistance to increase fuel economy by some 5 to 10 percent.
The company said that it stopped production of the affected vehicles, both Mitsubishi and Nissan will suspend sales and discuss compensation for affected owners.
The probe also found that other models in the Japanese market were tested via the wrong evaluation. Mitsubishi plans to convene a panel of external exports to conduct an investigation, which will include vehicles manufactured for overseas markets.