The NHTSA's investigation of the BMW 7-Series is one step closer to a recall.

The National Highway Traffic Safety Administration is stepping up its investigation of 122,000 BMW 7-Series models for a possible transmission flaw. The probe covers vehicles from the 2002-2008 model years.

The NHTSA first launched an investigation into the BMW 7-Series last August after receiving customer complaints of rollaway vehicles. Since then the NHTSA has received 50 more complaints of rollaway accidents - including 16 that involved crashes resulting in 5 injuries - prompting the safety agency to upgrade its probe.

The complaints allege a fault in the 7-Series electronic transmission. The 2002-08 7-Series came equipped with BMW's "Comfort Access" electronic access and ignition system, which BMW says was designed to put the vehicle in 'Park' when the ignition was turned off. However, that system appears to have some sort of flaw that allows the gearbox to slide into neutral as all incidents have occurred after the driver has turned off the vehicle's engine.

The NHTSA has yet to announce a recall for the 2002-08 7-Series, but the upgrade of the investigation indicates that one is likely on the way.