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U code network High severity

U1685 U1685: ECM-BCM Communication Failure

The OBD2 code U1685 indicates a communication failure between the Engine Control Module (ECM) and the Body Control Module (BCM), suggesting that these two modules are unable to exchange data properly

Definition

The OBD2 code U1685 indicates a communication failure between the Engine Control Module (ECM) and the Body Control Module (BCM), suggesting that these two modules are unable to exchange data properly

Common causes

  • Faulty ECM (Engine Control Module)
  • Faulty BCM (Body Control Module)
  • Damaged wiring or connectors between ECM and BCM
  • Corroded connectors
  • Poor ground connections
  • Software issues or programming errors
  • Electrical interference or noise
  • Blown fuses related to ECM or BCM communication

Common misdiagnoses

  • Faulty ECM (Engine Control Module)
  • Faulty BCM (Body Control Module)
  • Wiring issues or shorts in communication lines
  • Corrupted software or firmware in ECM/BCM
  • Faulty sensors or actuators
  • Battery or power supply issues
  • Grounding problems
  • Other communication protocol failures (e.g., CAN bus issues)

Troubleshooting steps

  1. 1. Check for Additional Codes

    Use an OBD-II scanner to check for any other trouble codes that may be present. Addressing other codes may help in diagnosing the issue

  2. 2. Inspect Wiring and Connectors

    Visual Inspection: Check the wiring harness and connectors between the ECM and BCM 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 damaged

  4. 4. Check Power and Ground

    Verify that the ECM and BCM are receiving proper power and ground. Use a multimeter to check voltage at the connectors

  5. 5. Ensure that the ground connections are secure and free of corrosion

  6. 6. Test Communication Lines

    Use a scan tool to check if the ECM and BCM can communicate with each other. If one module is not responding, it may indicate a fault in that module or the communication line

  7. 7. Check for continuity in the communication lines (CAN bus) between the ECM and BCM

  8. 8. Inspect for Short Circuits or Open Circuits

    Check for any short circuits or open circuits in the wiring between the ECM and BCM. This may require a wiring diagram for reference

  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 ECM or BCM

  10. 10. Test the Modules

    If all wiring and connections are good, the ECM or BCM may be faulty. Testing the modules individually or swapping them with known good units (if available) can help identify the faulty component

  11. 11. Clear Codes and Test Drive

    After performing repairs, clear the trouble codes and take the vehicle for a test drive to see if the code returns

  12. 12. Consult Technical Service Bulletins (TSBs)

    Check for any TSBs related to the U1685 code for your specific vehicle make and model. Manufacturers may have specific recommendations or known issues

  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 your vehicle's specific systems. By following these troubleshooting steps, you should be able to identify and resolve the communication failure indicated by the U1685 code