Defect
On certain vehicles, a problem inside the transmission could cause the left-front axle shaft to separate from the transmission. If this happens, there would be a loss of power to the wheels. This could also cause the vehicle to roll away while parked, if the parking brake isn't used. Note: This problem could cause a grinding or clicking noise from the front of the vehicle.
Safety Risk
A loss of power to the wheels could increase the risk of a crash. Additionally, a parked vehicle that moves unintentionally could create a risk of a crash or an injury.
Remedy
General Motors will notify owners by mail and instruct you to take your vehicle to a dealership to replace the transmission sun gear.