Possible Causes
WARNING: This page is about a different car, the 2005 Jeep Liberty. However, it is still accessible from the selected car via links, so may be relevant.
BACK UP LAMP GROUND CIRCUIT OPEN
BACKUP LAMP FEED CIRCUIT OPEN
FUSED IGNITION SWITCH OUTPUT CIRCUIT OPEN
BACKUP LAMP FEED CIRCUIT SHORT TO GROUND
OPEN BACKUP LAMP BULB(S)
TRANSMISSION RANGE SENSOR