The National Highway Traffic Safety Administration began investigating the cars last August. The agency has upgraded the probe to an engineering analysis, which is a step toward a recall.
The investigation covers nearly 122,000 BMWs from the 2002 through 2008 model years.
The cars have push-button start and electronic transmission controls. In some cases the owners may think the cars are in park when they actually are in neutral. The safety agency said in documents on its website Monday that the cars can roll away unexpectedly and crash.
BMW and investigators have received 50 complaints about the problem.
Messages seeking comment from BMW were not immediately returned.
