WARNING: This page is about a different car, the 2012 RAM Pickup and 2012 RAM Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.
Possible Causes
REAR DIFFERENTIAL POSITION SENSOR (WIRING, CONNECTOR AND/OR TERMINAL CONDITION)
REAR DIFFERENTIAL POSITION SENSOR
(T527) REAR LOCKER SENSOR SENSE CIRCUIT FOR AN OPEN