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U0120Lost Communication With Starter / Generator Control Module

The OBD2 code U0120 indicates a loss of communication between the vehicle's control module and the starter/generator control module, which can affect the starting and charging systems

Definition

The OBD2 code U0120 indicates a loss of communication between the vehicle's control module and the starter/generator control module, which can affect the starting and charging systems

Common causes

  • Faulty Starter/Generator Control Module
  • Damaged wiring or connectors
  • Poor electrical connections
  • Blown fuses
  • Faulty engine control module (ECM)
  • Corroded terminals
  • Software issues or glitches
  • Battery voltage issues
  • Grounding problems
  • Intermittent faults in the communication network

Common misdiagnoses

  • Faulty Starter/Generator Control Module
  • Wiring issues or damaged connectors
  • Faulty Engine Control Module (ECM)
  • Battery or charging system problems
  • Faulty ignition switch
  • Corroded or loose ground connections
  • Faulty sensors related to the starting system
  • Issues with the vehicle's CAN bus communication system

Troubleshooting steps

  1. 1.Check for Additional Codes

    Use an OBD-II scanner to check for any other related trouble codes. This can provide more context and help identify if there are other issues present

  2. 2.Inspect Wiring and Connectors

    Visual Inspection: Check the wiring harness and connectors related to the Starter/Generator Control Module for any signs of damage, corrosion, or loose connections

  3. 3.Connector Pins

    Ensure that the pins in the connectors are not bent, corroded, or pushed back

  4. 4.Check Power and Ground

    Power Supply: Verify that the Starter/Generator Control Module is receiving the correct voltage. Use a multimeter to check the power supply to the module

  5. 5.Ground Connections

    Ensure that the ground connections for the module are secure and free of corrosion

  6. 6.Inspect the Starter/Generator Control Module

    If the wiring and connections are intact, the issue may lie within the Starter/Generator Control Module itself. Check for any signs of physical damage or overheating

  7. 7.Test Communication Lines

    Use a scan tool to check if the module is communicating with other modules in the vehicle. If other modules are also not communicating, it may indicate a network issue

  8. 8.Check the CAN (Controller Area Network) bus for continuity and proper operation

  9. 9.Check for Software Updates

    Sometimes, communication issues can be resolved with a software update. Check with the manufacturer for any available updates for the vehicle’s ECU

  10. 10.Perform a Hard Reset

    Disconnect the vehicle's battery for a few minutes to reset the system. Reconnect and see if the code reappears

  11. 11.Inspect Related Components

    Check other components that may interact with the Starter/Generator Control Module, such as the battery, alternator, and any related sensors

  12. 12.Consult Technical Service Bulletins (TSBs)

    Look for any TSBs related to the specific make and model of the vehicle. Manufacturers may have issued guidance on common issues related to U0120

  13. 13.Seek Professional Help

    If the issue persists after performing the above steps, it may be necessary to consult a professional mechanic or technician who has experience with the specific vehicle and its systems.Conclusion Troubleshooting a U0120 code involves a systematic approach to check for communication issues, inspect wiring and connections, and verify the functionality of the Starter/Generator Control Module. Always ensure safety precautions are taken when working on vehicle electrical systems