Had the SOS warning along with High Battery Drain message. After triangulation (trying resets, pulling fuses, etc.), determined that the TCU had failed. Rather than purchasing the fiber jumper, I purchased a replacement TCU with the same software and hardware versions (made just a few months apart). Swapped the units and BT is back and the SOS and High Battery Drain warning are gone. It's an easy swap. The only challenge is removing the clips from the wire connectors.