U0100
NetworkModule Communicationcritical severityLost Communication with ECM/PCM
What U0100 Means
The diagnostic system cannot communicate with the Engine Control Module.
Symptoms
- Multiple warning lights
- Engine may not start
- Many systems inoperative
- Cannot read engine codes
Common Causes
- PCM power or ground failure
- CAN bus wiring issue
- PCM failure
- Fuse blown
- Wiring harness damage
Diagnostic Steps
- Check PCM fuses
- Test PCM power and ground circuits
- Check CAN bus wiring to PCM
- Try communicating with other modules
- Inspect wiring harness
Where to start: Check fuses and power supply to PCM first. CAN bus issue is second most common.
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