Think of the CAN (Controller Area Network) as a shared party line where each module takes turns announcing its status. The monitoring module (often the PCM or a gateway) expects to hear the TCCM's "heartbeat" at regular intervals. When those updates go quiet for longer than the vehicle allows, U0102 is stored. The silence points to one of three things: the TCCM has lost power, its network wiring is broken, or its internal transceiver has stopped working.