U1644 – Lost Communication with Body Control Module (BCM).

The ODBII code U1644 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.

The severity of ODBII code U1644 is generally considered moderate to severe.

Common Causes For: U1643 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 U1644 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 OBD-II code U1644, 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 damaged.
• 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: 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 are any environmental factors (moisture, extreme temperatures) that could be affecting the BCM or its connections.
• 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.
• 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. By following these steps, you should be able to identify the cause of the U1644 code and take appropriate action to resolve the communication issue with the Body Control Module.