U1643 – Lost Communication with Body Control Module (BCM).

The ODBII code U1643 indicates that there is a communication failure 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 U1643 is generally considered moderate to severe.

Common Causes For: U1642 U1642: Body Control Module Communication Failure

• Faulty Body Control Module (BCM)
• Damaged wiring or connectors
• Poor ground connection
• Corroded terminals
• Faulty communication network (CAN bus issues)
• Blown fuses
• Software issues or programming errors
• Intermittent electrical connections

Common misdiagnosis for U1643 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
• Battery or charging system problems
• Faulty ignition switch
• Grounding issues in the electrical system
• Intermittent communication faults due to environmental factors

Common Troubleshooting Steps

When dealing with the OBD-II code U1643, 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 Other Codes: Use an OBD-II scanner to check for any additional trouble codes. Sometimes, other codes can provide context or indicate 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 or water intrusion.
• **Reprogramming: If the BCM has been replaced, ensure that it has been properly programmed to the vehicle.
• Test Communication Lines: **CAN Bus: Use a scan tool to check the communication on the CAN bus. If other modules are not communicating, there may be a fault in the bus itself.
• **Scope Testing: If available, use an oscilloscope to check for proper signal patterns on the communication lines.
• Check for Short Circuits: Inspect the wiring for any short circuits to ground or power that could affect communication with the BCM.
• Look for Environmental Factors: Consider if there have been any recent changes to the vehicle, such as aftermarket installations, that could affect the BCM or its communication.
• 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 returns.
• Consult Technical Service Bulletins (TSBs): Check 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, consider replacing it. Ensure proper programming and configuration after replacement.1
• Seek Professional Help: If you are unable to resolve the issue, it may be best to consult a professional mechanic or dealership with experience in diagnosing and repairing BCM-related issues.Conclusion Troubleshooting a U1643 code can be complex, as it often involves multiple systems within the vehicle. Following these steps methodically can help isolate the problem and lead to a resolution. Always ensure safety precautions are taken when working on vehicle electronics.