According to the suit, which was filed in a District Court in Los Angeles last week, the extended-range i3, known as the i3 REx, can reduce power to unsafe levels without warning. Here’s what the suit, filed by MLG Automotive Law, has to say:

“If the car is under any kind of significant load (such as going up a hill, or loaded with passengers), the speed of the car will dramatically decrease as the battery charge diminishes.

“The lawsuit alleges that this can result in the car slowing to speeds of 45 miles per hour on the freeway, without warning.”

2014 BMW i3, 2013 Frankfurt Auto Show

The reduced acceleration under high-stress, low-charge situations is a problem High Gear Media staff have experienced. The 34-horsepower 2-cylinder range extender (shown above) is simply not powerful enough to maintain the car’s performance in all situations when the battery is depleted.

The cause is due to the i3 REx’s programming that requires it to exhaust essentially all of its battery capacity before the range extender switches on. According to Green Car Reports, this is so the car can qualify as a battery-electric vehicle (BEVx) under California zero-emission vehicle rules.

BMW updated the i3 REx with a software tweak last year. The update included a warning that flashes onto the car’s dash about potentially reduced performance when the car’s battery drops to 2 percent.

MLG Automotive Law says its goal with the suit is for BMW to halt the sale of i3s until they, as well as all existing cars, are “repaired at BMW’s expense.” MLG is also asking for compensation from BMW for each owner.