The National Highway Traffic Safety Administration (NHTSA) has launched a safety probe in response to owner reports of fires in Chevrolet Bolt EV electric cars.

Two owner-submitted reports—one each for a 2018 and 2019-model-year Bolt EV—allege that the cars caught fire under the rear seat while parked and unattended, according to an NHTSA document.

Additional research conducted by the agency's Office of Defects Investigation (ODI) found a 2017 Bolt EV with a similar burn pattern in the rear-seat area, according to the document.

In all three cases, fire damage appeared to be concentrated in a battery-pack compartment, with fire penetration into the passenger compartment from under the rear seat, according to the findings of the government office. Smoke-inhalation injuries were reported in one case.

The root cause of the fires is unknown, and the ODI is opening a "preliminary evaluation" into the matter.

2019 Chevrolet Bolt EV

2019 Chevrolet Bolt EV

Other electric cars have also been investigated recently over alleged fires.

Last year, the NHTSA asked Tesla about its battery-management software after reported fires in the Model S and Model X.

There have also been a number of incidences relating to Hyundai Kona Electric charging—resulting in a recently announced recall that hasn't yet been detailed for North America.

Reports of Bolt EV fires follow a familiar pattern. Most reported EV fires occur when the vehicle is parked and unattended—and during charging.

Meanwhile, Chevy has many upgrades on the way for the 2022 model year, including styling changes, new front seats, and a new sensor array to support more sophisticated driver aids. A Bolt EUV crossover variant will follow a refreshed version of the standard Bolt EV to showrooms—but won't get all-wheel drive.