Question

I have a 2011 Cadillac Escalade Hybrid with code U0100 and the car is not starting

Answer 1

U0100 Serial data circuit.communication loss.

Serial data circuit the control modules communicate with each other. When a control module stops communicating on the serial data it can be from power to ground issues or connection issues. Just because you have PU0100 as a DTC doesn't necessarily mean a control module failure, this can come from low battery conditions to interrupting power like changing a battery,

Answer 2

U0100 CADILLAC Code - Lost Communication With Engine Control Module
Read more: https://www.autocodes.com/u0100_cadillac.html