U1641 – Lost Communication with Body Control Module (BCM).

The ODBII code U1641 indicates a loss of communication between the vehicle’s control module and the Body Control Module (BCM), which may affect various electrical functions and systems in the vehicle.

The severity of ODBII code U1641 is generally considered moderate to high.

Common Causes For: U1640 Lost Communication with Body Control Module (BCM).

• 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

Common misdiagnosis for U1641 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 Powertrain Control Module (PCM)
• Malfunctioning Instrument Cluster
• Problems with the CAN bus system
• Low battery voltage or power supply issues
• Faulty sensors or actuators related to the BCM
• Software or firmware issues in the BCM
• Grounding issues in the electrical system

Common Troubleshooting Steps

When dealing with the OBD-II code U1641, 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 the 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.
• Check Power and Ground: **Power Supply: Verify that the BCM is receiving the correct voltage. Use a multimeter to check the power supply at the BCM connector.
• **Ground Connections: Ensure that the ground connections for the BCM are secure and free of corrosion.
• Inspect the BCM: **Physical Condition: Check the BCM for any signs of physical damage, such as cracks or burn marks.
• **Reprogramming: If the BCM has been replaced, ensure that it has been properly programmed to the vehicle.
• Test Communication Lines: **CAN Bus: If your vehicle uses a CAN bus system, check the communication lines for continuity and proper signal. You may need an oscilloscope to check for data transmission.
• **Other Modules: Check if other modules in the vehicle are communicating properly. If they are also having communication issues, it may indicate a broader network problem.
• Check for Short Circuits: Use a multimeter to check for short circuits in the wiring harness that could affect communication with the BCM.
• Inspect Fuses: Check the fuses related to the BCM and other modules. A blown fuse can interrupt communication.
• Perform a Hard Reset: Disconnect the battery for a few minutes to reset the vehicle’s electronic systems. Reconnect and see if the code reappears.
• Scan for Updates: Check if there are any software updates available for the BCM or other related modules. Sometimes, manufacturers release updates to fix communication issues.
• Consult Technical Service Bulletins (TSBs): Look for any TSBs related to the U1641 code for your specific vehicle make and model. Manufacturers may have documented common issues and fixes.1
• Seek Professional Help: If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or dealership for further diagnosis. They may have specialized tools and knowledge to address complex issues. By following these steps, you should be able to identify the root cause of the U1641 code and take appropriate action to resolve it.