U0120
NetworkModule Communicationmoderate severityLost Communication with Starter/Generator Module
What U0120 Means
Cannot communicate with the integrated starter-generator in start-stop or mild hybrid vehicles.
Symptoms
- Start-stop system disabled
- Engine will not auto-restart
- Mild hybrid assist not available
- Warning message displayed
Common Causes
- Starter-generator module failure
- CAN bus wiring
- Module power loss
- Belt-driven starter-generator fault
Diagnostic Steps
- Check module fuse
- Test power and ground
- Check CAN wiring
- Test starter-generator operation
- Inspect drive belt condition
Where to start: Check power supply and belt condition on belt-driven starter-generators.
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