WOMS
U code network High severity

U2120 U2120: "BCM Communication Failure

The OBD2 code U2120 indicates a communication failure between the Body Control Module (BCM) and other modules in the vehicle's network, suggesting a disruption in data exchange

Definition

The OBD2 code U2120 indicates a communication failure between the Body Control Module (BCM) and other modules in the vehicle's network, suggesting a disruption in data exchange

Common causes

  • Faulty Body Control Module (BCM)
  • Damaged wiring or connectors
  • Poor ground connections
  • Corroded terminals
  • Software issues or programming errors
  • Malfunctioning communication network (CAN bus)
  • Other module failures affecting communication
  • Battery voltage issues

Common misdiagnoses

  • Faulty Body Control Module (BCM)
  • Wiring issues or shorts in the communication lines
  • Faulty or corroded connectors
  • Issues with other control modules (e.g., PCM, ECM)
  • Software or firmware issues in the BCM
  • Battery or power supply problems
  • Grounding issues
  • Faulty sensors or actuators related to the BCM
  • Intermittent communication issues due to environmental factors
  • Incorrectly configured aftermarket accessories or modifications

Troubleshooting steps

  1. 1. Check for Additional Codes

    Use an OBD-II scanner to check for any other trouble codes that may be present. Other codes can provide additional context for the issue

  2. 2. Inspect Wiring and Connectors

    Visual Inspection: Check the wiring harness and connectors related to the BCM for any signs of damage, corrosion, or loose connections

  3. 3. Connector Pins

    Ensure that the pins in the connectors are not bent or corroded

  4. 4. Test the BCM

    Power and Ground: Verify that the BCM is receiving proper power and ground. Use a multimeter to check voltage at the BCM connector

  5. 5. Module Functionality

    If possible, test the BCM in another vehicle or replace it with a known good unit to see if the problem persists

  6. 6. Check Communication Lines

    CAN Bus: If your vehicle uses a CAN bus system, check the communication lines for continuity and proper voltage levels. Look for shorts or open circuits

  7. 7. Scope Testing

    Use an oscilloscope to check the data lines for proper signal patterns

  8. 8. Inspect Other Modules

    Since the BCM communicates with other modules, check those modules for faults. Look for codes or issues in related systems (e.g., lighting, security, etc.)

  9. 9. Check for Software Updates

    Sometimes, a software update for the BCM or other modules can resolve communication issues. Check with the manufacturer for any available updates

  10. 10. Clear Codes and Test Drive

    After performing checks and repairs, clear the codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns

  11. 11. Professional Diagnosis

    If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership with advanced diagnostic tools.Conclusion Troubleshooting a U2120 code can involve a combination of visual inspections, electrical testing, and module checks. It’s important to approach the diagnosis methodically to identify the root cause of the communication failure