2001 Cadillac Catera ETCBM

A U2108 is a communication fault, It involves either the EBTCM(abs module), Trans control module, engine control module, or wiring in between. The fault chart points to the ebtcm if the u2108 resets, and is the only code. I would first see if a scan tool can communicate with all modules. If so, check the wiring between for opens, shorts to ground, and poor terminal tension/connections. The ebtcm is probably not cheap, nor is it easy to access.