Engineers at General Motors are blaming the issue on a liquid solution that cools that car's batteries.
They're working on making structural changes to strengthen the car's T-shaped battery pack. They are also looking at ways to bolster the car's body to make it more resistant to side-impact crashes.
A person briefed on the matter told The Associated Press that the coolant itself did not catch on fire, but it crystallized and created an electrical short that apparently sparked the fires. The person did not want to be identified because the findings are not final.
Last month, the National Highway Traffic Safety Administration launched an investigation into Volt battery fires, which occurred from seven days to three weeks after crash tests by the agency.
According to the source, the chemical reaction that stores and discharges energy from the battery is not the culprit. They believe that if they can stop the coolant from leaking, they can stop the fires.
Meanwhile, Transportation Secretary Ray LaHood said the Volt is safe to drive, even though the government is still investigating the fires.
The Associated Press contributed to this report.