Before replacing any module, perform a full system voltage stabilization (charge battery, clean main grounds) and verify no aftermarket devices (remote starters, trackers) are corrupting the CAN bus.

When code U2102-00 appears, it means the receptionist (BCM) or another crucial module has sent a message, but the response was either gibberish, missing entirely, or came from a module that "doesn't belong" in that specific office configuration.