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U code network High severity

U0129 Lost Communication With Brake System Control Module

The OBD2 code U0129 indicates that there is a loss of communication between the vehicle's control module and the brake system control module, which may affect the operation of the braking system

Definition

The OBD2 code U0129 indicates that there is a loss of communication between the vehicle's control module and the brake system control module, which may affect the operation of the braking system

Common causes

  • Faulty Brake System Control Module
  • Damaged wiring or connectors
  • Corroded terminals
  • Poor ground connection
  • Faulty ABS module
  • Software issues or updates needed
  • Blown fuses
  • Intermittent electrical connections
  • Malfunctioning power supply to the module

Common misdiagnoses

  • Faulty Brake System Control Module
  • Wiring Issues or Short Circuits
  • Faulty ABS Module
  • Faulty Engine Control Module (ECM)
  • Faulty Body Control Module (BCM)
  • Corroded Connectors
  • Battery or Charging System Issues
  • Faulty Wheel Speed Sensors
  • Software or Calibration Issues
  • Faulty Powertrain Control Module (PCM)

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 the Wiring and Connectors

    Visual Inspection: Check the wiring harness and connectors related to the brake system 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 damaged

  4. 4. Check the Brake System Control Module

    Module Functionality: If possible, test the brake system control module to ensure it is functioning correctly. This may require specialized diagnostic equipment

  5. 5. Power and Ground

    Verify that the module is receiving the correct power and ground signals. Use a multimeter to check voltage and ground continuity

  6. 6. Inspect the CAN Bus System

    Communication Lines: Since U0129 is a communication-related code, check the Controller Area Network (CAN) bus lines for continuity and integrity. Look for shorts, opens, or high resistance in the wiring

  7. 7. Termination Resistors

    Ensure that the CAN bus termination resistors are present and functioning correctly

  8. 8. Check for Intermittent Issues

    Temperature and Vibration: Sometimes, issues can be intermittent. Check if the problem occurs under specific conditions, such as temperature changes or vibrations

  9. 9. Perform a System Reset

    Clear Codes: Clear the trouble codes using the OBD-II scanner and see if the code returns after a test drive. This can sometimes reset communication issues

  10. 10. Inspect Related Components

    ABS Module: Since the brake system control module is often part of the ABS system, check the ABS module and its connections

  11. 11. Other Modules

    Check other modules that communicate with the brake system control module, as issues in these modules can affect communication

  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 U0129

  13. 13. Professional Diagnosis

    If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership. They may have access to advanced diagnostic tools and resources

  14. 14. Replace Faulty Components

    If a faulty brake system control module or related component is identified, replace it as necessary. By following these steps, you should be able to identify the root cause of the U0129 code and take appropriate action to resolve the issue. Always ensure safety when working on vehicle systems, especially those related to braking