Originally Posted by jwikoff99
You could try taking out the bulbs and cleaning the sockets. That might just fix it.
Also check that you have the correct number of bulb at each location back there; a lower-wattage bulb may draw so little power that the Adaptive Lamp Monitor Unit thinks it'* burned out. You can check out http://www.sylvania.com/auto/carapp/
for a handy lookup listing of bulb specs for your car.
Also don't forget your license-plate lamp(*) and rear side marker bulbs. The rear side markers are snuggled into the extreme outer corners of the red lenses and may be easy to miss.
Finally, turn on your taillights, then have an assistant step on the brake. Any brake lights that go out instead of getting brighter have a bad ground connection at that socket. (Under those conditions, one circuit is using the other for grounding, so when both Tail and Brake circuits are hot, the bulb in the problem socket goes out instead.)