OBD-II CODE / Network
U0100 · Lost communication with ECM or PCM
A module reported that it lost communication with the engine or powertrain computer.
Who recorded the fault?
A network code is a report from a module that stopped receiving expected messages. An all-module scan can show whether several modules lost contact or only one did.
Keep the battery and wiring context
Note a recent dead battery, jump-start or electrical repair. Power, grounds, connectors and network wiring should be checked using the vehicle wiring information before replacing a control module.
A vehicle-specific example
GM’s diagnostic information groups U0100 with other possible network codes on covered vehicles. That combination can give a technician more context than U0100 on its own.