Nikola is voluntarily recalling 209 Tre battery-electric trucks, after an investigation into battery pack fires that occurred at its facilities.

An independent investigation found a coolant leak inside a single battery pack was to blame for a June 23 truck fire at Nikola’s headquarters. Those findings were further corroborated by a second fire on an engineering truck at Nikola’s Coolidge, Ariz., plant on Aug. 10.

Foul play, initially thought to be the cause of the fires, is no longer suspected.

Nikola is voluntarily filing a recall with the National Highway Traffic Safety Administration and is placing a temporary hold on new BEV sales until a resolution is in place. Tre BEV trucks can remain in operation, but the company advises customers to place the Main Battery Disconnect switch into the ‘On’ position at all times, and consider parking outdoors to allow over-the-air updates and better connectivity with Nikola’s Fleet Command telematics.

The truck maker notes there have only been two known incidents out of more than 3,100 battery packs on trucks produced to date.

“At Nikola we take safety very seriously,” Nikola CEO Steve Girsky said n a press release. “We stated from the beginning that as soon as our investigations were concluded we would provide an update, and we will continue our transparency as we learn more.”

The voluntary recall and investigation into the causes of the fires will not affect Nikola’s rollout of hydrogen-fuel-cell-electric trucks, the company added. Those trucks are in production now, with deliveries slated for the third quarter.