Code
U0100
Network
Lost communication with engine control module
Another module cannot communicate with the engine computer over the CAN bus.
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Most likely causes
- Disconnected or corroded connector
- CAN bus wiring fault
- Dead ECM fuse
- Failed ECM
Symptoms you may notice
- Many warning lights
- Engine may not start
- Scan tool cannot talk to ECM
Checks to run
- Check ECM power and grounds
- Test CAN bus resistance and continuity
- Inspect connectors
Tools you may need
Multimeter
OBD-II scanner
Always diagnose before replacing. Codes share symptoms; confirm the cause with measurements before buying parts.