BMW is facing claims that its i3 may be defective.

BMW is facing a class action lawsuit over allegations that it's i3 Range Extender model can suffer from a sudden loss of drivetrain power.

The suit, filed by MLG Automotive Law in Los Angeles earlier this week, covers only i3 models equipped with BMW's Range Extender package, which adds a two-cylinder gas engine to supplement the city car's electric drivetrain. BMW says the Range Extender package adds about another 70 miles to the i3's 80 mile EV range.

However, the suit claims that the gas engine doesn't supply enough energy to keep the electric drivetrain running optimally, resulting in a loss of power. The suit alleges that the defect can cause the i3 to suddenly slow down from highway speeds to just 45mph without warning.

"The BMW i3 Range Extender feature is a dangerous instrumentality to the owners of the vehicles and to other motorists on the road," said Jonathan Michaels, founding member of MLG Automotive Law. "Having a sudden and unexpected loss of power in a motor vehicle can result in a catastrophic situation for all those on the road. These cars are dangerous and should not be driven."

MLG wants BMW to fix the problem and halt all sales of the i3 until a solution is discovered. The law firm is also seeking an undisclosed monetary compensation "for all the owners of the vehicles, who were not told of the serious safety defect."

BMW has not issued any recalls for the i3 related to the claims made in the lawsuit.