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Lost Communication With ECM/PCM
🔴 CRITICAL — STOP DRIVING NETWORK · CAN Bus
A control module on the CAN bus cannot communicate with the Engine Control Module.
What You'll Notice
- Multiple warning lights across clusters — ABS, SRS, traction control all on simultaneously
- Instrument cluster gauges dropping to zero
- Engine may not start
- Transmission stuck in limp mode
Probable Causes
- CAN bus wiring fault — chafed, corroded, or accidentally cut harness
- Failed PCM / ECM module
- Bad PCM ground or power supply circuit
- Corroded battery terminals causing intermittent voltage drop on CAN network
Direct Repair Steps
- Check battery voltage and terminal connections first — low voltage causes false U-codes
- Verify PCM power and ground circuits with a DVOM (should read battery voltage and <0.1 Ω ground resistance)
- Inspect main engine harness connectors at PCM for corrosion or pushed-back pins
- Use advanced scan tool to check CAN bus health; look for bus-off errors indicating a module pulling the bus low
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Check PriceQuick answers
What does U0100 mean?
A control module on the CAN bus cannot communicate with the Engine Control Module.
Is U0100 serious?
It depends on the system and symptoms, but the page ranks the severity and likely causes so you can decide whether to stop driving or continue with caution.
What should I buy before troubleshooting U0100?
A reliable OBD2 scanner helps confirm the code, read live data, and avoid guessing before repairs.