i feel the need to add to this as this issue presented itself to me a little while back and was quite frustrating.
there are relays that run those lights, i had a bad one and after replacement the code would still not clear. did not have the maintenance password. the software version was an old one and would not automatically reset the code after the circuit was repaired, the dealer had to come and reset maint. password and installed the latest software, now once the circuit is repaired the code automatically clears.

superiorlift at windstream.net, the troubleshooting for a tail light is pretty straight forward, you check the light bulb and wires to them.

Thanks for your help. Can you send troubleshooting procedures to [email address removed]

Back up light driver output oorh, check backup lights.
Can send the troubleshooting procedures to an e-mail address