Mitsubishi Motors announced the findings of its investigation into the recent fires involving its lithium-ion batteries.

In a dry press release, Mitsubishi Motors announced the findings of its investigation into the recent fires involving its lithium-ion batteries. In early April, Mitsubishi suspended production of the Outlander PHEV and some models of the i-MiEV, after two separate incidents in Japan, one in a battery inspection room at the company’s Mizushima Plant and one at a dealership in Yokohama (there were no injuries, and little damage).

Here’s what the company had to say:

The joint investigation revealed that the battery cell defect originated from a part of the supplier’s manufacturing line, resulting in short-circuited battery cells. The defect occurred in a screening process that was added to the manufacturing line in December 2012. It was found that during this screening process the shape of an internal part of the battery cell was altered and some microscopic contaminants were generated as a result of battery cells being exposed to excessive force.

The screening process where the defect was occurring has been removed.

As reported by Automotive News, the potential defect affects about 4,000 Outlander PHEVs, and about 100 i-MiEVs, mostly in Japan and Europe. Mitsubishi has told affected i-MiEV owners not to drive them, and told drivers of the Outlander PHEV, which is sold only in Japan, not to use hybrid and EV modes (affected drivers have been offered loaner vehicles). Mitsubishi plans to issue a recall in Japan next month.

The problem started last December, when a new screening process was introduced to the production line. The supplier, Lithium Energy Japan, has dropped the screening process that caused the defects, and the two companies are working on an improved process. Mitsu doesn’t expect the issue to delay next year’s US launch of the Outlander PHEV.

Earlier this week, the company recalled 3,839 Outlander PHEVs in Japan for an unrelated problem with the motor control software.

Sources: Mitsubishi, Automotive News