U2129 – Lost Communication with the Battery Energy Control Module (BECM).

The ODBII code U2129 indicates that there is a loss of communication between the vehicle’s control module and the Battery Energy Control Module (BECM), which may affect battery management and performance.

The severity of ODBII code U2129 is typically considered moderate to high.

Common Causes For: U2128 Lost Communication with the Steering Angle Sensor.

• Faulty Battery Energy Control Module (BECM)
• Damaged wiring or connectors
• Poor ground connections
• Low battery voltage
• Corroded terminals
• Faulty communication lines
• Software issues or updates needed
• Malfunctioning powertrain control module (PCM)

Common misdiagnosis for U2129 Lost Communication with the Battery Energy Control Module (BECM).

• Faulty Battery
• Bad Battery Connections
• Defective Alternator
• Wiring Issues
• Faulty Power Distribution Module
• Malfunctioning Engine Control Module (ECM)
• Incorrectly Installed Aftermarket Accessories
• Corroded Connectors
• Software Issues or Updates Needed
• Faulty Ground Connections

Common Troubleshooting Steps

When dealing with the OBD-II code U2129, which indicates “Lost Communication with the Battery Energy Control Module (BECM),” there are several common troubleshooting steps you can follow to diagnose and potentially resolve the issue. Here’s a structured approach:

• Check for Additional Codes: Use an OBD-II scanner to check for any other trouble codes that may be present. This can provide more context and help identify related issues.
• Inspect the Wiring and Connectors: **Visual Inspection: Check the wiring harness and connectors leading to the BECM for any signs of damage, corrosion, or loose connections.
• **Connector Pins: Ensure that the pins in the connectors are not bent, corroded, or pushed back.
• Test the BECM: If accessible, test the BECM for proper operation. This may involve checking the power and ground circuits to the module.
• Use a multimeter to verify that the BECM is receiving the correct voltage and ground.
• Check for Communication Issues: Use a scan tool to check if the BECM is communicating with other modules in the vehicle. If other modules are also not communicating, it may indicate a network issue.
• Inspect the CAN (Controller Area Network) bus wiring for shorts, opens, or other faults.
• Inspect the Battery and Charging System: Ensure that the battery is in good condition and fully charged. A weak or failing battery can cause communication issues.
• Check the alternator and charging system to ensure they are functioning properly.
• Reset the Codes: After performing inspections and repairs, clear the trouble codes using the OBD-II scanner and see if the code returns after a test drive.
• Check for Software Updates: In some cases, the vehicle manufacturer may have released software updates for the BECM or other modules. Check for any available updates that may address communication issues.
• Consult Technical Service Bulletins (TSBs): Look for any TSBs related to the specific make and model of the vehicle. Manufacturers may have documented known issues and solutions for U2129.
• Professional Diagnosis: If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership. They may have specialized tools and knowledge to diagnose complex communication issues.Conclusion Troubleshooting the U2129 code involves a systematic approach to check for wiring issues, module functionality, and communication integrity. By following these steps, you can often identify the root cause of the problem and take appropriate action to resolve it.