The official notice
Defect
Under certain conditions, a software problem could cause the transmission control module not to work correctly. As a result, there could be reduced power to the wheels, the transmission could shift harshly and/or the rear wheels could lock up. Additionally, at low speeds, this problem could cause the vehicle to move in an unintended direction. Note: This recall only affects vehicles with certain engine and transmission combinations.
Safety Risk
Rear wheels that lock suddenly could cause a loss of control and increase the risk of a crash. Additionally, a vehicle that moves in the unintended direction could also increase the risk of a crash.
Remedy
General Motors will notify owners by mail and advise you to take your vehicle to a dealership to update the transmission control module software.