Handyjay .
I just find this for you . Without cd changer
1 input power to receiver unit in the trunk is missing check the 12 volt feed .
2 Fuse of the receiver unit in the trunk is open replace the 7.5 amp fuse
3 The bus cable [greywire] that comes to the head unit [dash mounted] to the receiever unit in the trunk mounted is not connected or is faulty
4 Receiver in trunk is defective .

With cd changer
1 Input power to receiver is missing 12 volt feed
2 Check the receiverunit for open fuse replace with a fuse rated 7.5 amp
3 Input power to dc changrrtrunk mounted is missing
4 Bus cable [grey colour] is defective or faulty.
5 Cd changer is defective disconnect cd from head unit if E2 code disappears replace cd changer
6 Receiver unit trunk mounted is faulty .
Good luck /