U0100 Lost communication with the engine control module
- System
- Network - modules not talking to each other
What U0100 means
The car's control modules talk to each other over a shared network, and each one expects regular messages from the others. This code's official name, "Lost communication with the engine control module", says the messages carrying the engine control module's data stopped arriving at whichever module was waiting for them, so what got measured is whether an expected message turned up in the time it was due - not any sensor value. The U at the front puts it in the network group: modules not talking to each other.
This is a standard code. It means the same thing on every make of vehicle.
What the program shows for U0100
The engine control module this code names is the one every gauge on the Dashboard is polled from, and the one the Full scan reads its Vehicle identity out of - VIN, Calibration and Verification number (CVN) - along with the Readiness monitors, the Freeze frame and the On-board self-tests. The CHECK ENGINE line on the Trouble Codes screen, with the lamp on or off and the stored and read counts beside it, is that same module's answer to a single request.
The Trouble Codes screen names the module the car lost contact with, from the engine and transmission modules to ABS, body, restraints and the instrument cluster, where the module is on its list. Look up a code does the same offline and says whether a code is standard or manufacturer-specific, and the Adapter traffic screen shows the raw requests and replies. Compare between two recordings shows whether the code is Gone, New or Still there.
See how the program shows a code →