U1649 – Lost Communication with Body Control Module (BCM).

The ODBII code U1649 indicates that there is a communication failure between the vehicle’s control module and the Body Control Module (BCM), which may affect various electrical systems and functions.

The severity of ODBII code U1649 is generally considered moderate to severe, as it indicates a communication issue that can affect multiple vehicle systems.

Common Causes For: U1648 U1648: “Communication Network Malfunction”

• Faulty Body Control Module (BCM)
• Damaged wiring or connectors
• Poor ground connections
• Corroded terminals
• Faulty communication network (CAN bus issues)
• Blown fuses
• Software or firmware issues in the BCM
• Intermittent electrical connections
• Other module failures affecting communication

Common misdiagnosis for U1649 Lost Communication with Body Control Module (BCM)”.

• Faulty Body Control Module (BCM)
• Wiring issues or shorts in the communication lines
• Faulty or corroded connectors
• Issues with the power supply to the BCM
• Malfunctioning other control modules
• Software or firmware issues in the BCM
• Problems with the vehicle’s battery or charging system
• Faulty ignition switch or related components

Common Troubleshooting Steps

When dealing with the OBD-II code U1649, which indicates “Lost Communication with Body Control Module (BCM),” 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 Wiring and Connectors: **Visual Inspection: Check the wiring harness and connectors leading to the BCM 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 BCM: **Power and Ground: Verify that the BCM is receiving proper power and ground. Use a multimeter to check voltage at the BCM connector.
• **Communication Lines: Check the CAN (Controller Area Network) bus lines for continuity and proper voltage levels.
• Check for Short Circuits: Inspect the wiring for any short circuits to ground or to other circuits that could affect communication with the BCM.
• Inspect Related Modules: Other modules on the CAN bus may be causing communication issues. Check for codes in other modules and ensure they are functioning properly.
• Perform a Hard Reset: Disconnect the vehicle’s battery for a few minutes to reset the BCM and other modules. Reconnect and see if the code reappears.
• Update or Reprogram the BCM: If the BCM is not functioning correctly, it may need to be reprogrammed or updated with the latest software from the manufacturer.
• Check for Environmental Factors: Ensure that there are no environmental factors (like water intrusion) affecting the BCM or its connections.
• Consult Technical Service Bulletins (TSBs): Look for any TSBs related to the specific make and model of the vehicle that may address known issues with the BCM.
• Replace the BCM (if necessary): If all other troubleshooting steps fail and the BCM is determined to be faulty, replacement may be necessary. Ensure that the replacement BCM is compatible with the vehicle.1
• Professional Diagnosis: If you are unable to resolve the issue, consider seeking help from a professional mechanic or dealership with experience in diagnosing BCM-related issues.Conclusion Always remember to take safety precautions when working on a vehicle’s electrical system. If you’re not comfortable performing these steps, it’s best to consult with a professional technician.