U1640 – Lost Communication with Body Control Module (BCM).

The ODBII code U1640 indicates a loss of communication between the vehicle’s control module and the Body Control Module (BCM), which can affect various electrical systems and functions.

The severity of ODBII code U1640 is generally considered moderate to high.

Common Causes For: U1639 Invalid or Missing Data for Vehicle Speed.

• Faulty Body Control Module (BCM)
• Damaged wiring or connectors
• Poor ground connection
• 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 U1640 Lost Communication with Body Control Module (BCM).

• Faulty Body Control Module (BCM)
• Wiring issues or shorts in the communication lines
• Faulty Instrument Cluster
• Defective Powertrain Control Module (PCM)
• Issues with the CAN bus system
• Battery or charging system problems
• Grounding issues
• Faulty sensors or actuators connected to the BCM

Common Troubleshooting Steps

When dealing with the OBD-II code U1640, 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 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 Communication: Use a scan tool to check if the BCM is communicating with other modules on the CAN bus. If other modules are also not communicating, the issue may be with the bus itself.
• **Scope Testing: If available, use an oscilloscope to check the CAN bus signals for proper voltage levels and signal integrity.
• 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 are any environmental factors (like moisture or extreme temperatures) that could be affecting the BCM or its connections.
• Reset the System: Clear the trouble codes using the OBD-II scanner and see if the code returns. Sometimes, a temporary glitch can cause communication issues.
• Consult Technical Service Bulletins (TSBs): Check for any TSBs related to the specific make and model of the vehicle. Manufacturers may have issued guidance on common issues related to 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 automotive technician who has experience with your vehicle’s make and model. By following these steps, you should be able to identify the root cause of the U1640 code and take appropriate action to resolve the communication issue with the Body Control Module.