Lost Communication With Starter/Generator Control Module
What does U0120 mean?
The U0120 code means the vehicle's onboard diagnostic system has detected: Lost Communication With Starter/Generator Control Module. This is a critical severity code.
Common Symptoms
- Stop/Start system not functioning
- Battery not charging properly
- Check Engine Light and battery warning light on
- Vehicle may stall or not restart after stopping
- Reduced fuel economy
Probable Causes (Ranked by Likelihood)
- Failed starter/generator control module Very High
- Damaged CAN bus wiring to starter/generator module High
- Belt-driven starter generator (BSG) failure Moderate
- Weak or failing 12V battery Moderate
- Corroded ground connection at starter/generator Low
Step-by-Step Diagnostic Procedure
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Scan for DTCs in all powertrain and charging system modules
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Check battery voltage and charging system output
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Inspect CAN bus wiring and connectors at the starter/generator module
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Verify power supply and ground at the module connector
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Test the belt-driven starter generator for proper operation
Frequently Asked Questions
Can I drive with code U0120?
You can drive short distances, but the battery may not charge properly, and the vehicle could stall. The Stop/Start system will also be disabled.
What causes U0120?
The most common cause is a failed starter/generator control module, especially on vehicles with Start/Stop systems. Wiring issues and weak batteries can also trigger this code.
Is U0120 expensive to fix?
Repairs range from $200 for wiring fixes to $1500 for a starter/generator replacement. Vehicles with eTorque or mild hybrid systems tend to be on the higher end.