U2644 – Lost Communication with Body Control Module (BCM) – Bus Off.

The ODBII code U2644 indicates that there is a communication failure between the vehicle’s control modules, specifically indicating that the Body Control Module (BCM) is not responding or is offline due to a bus communication issue.

The severity of ODBII code U2644 is generally considered moderate to severe.

Common Causes For: U2643 Lost Communication with the Steering Angle Sensor.

• Faulty Body Control Module (BCM)
• Damaged wiring or connectors in the communication circuit
• Short circuit or open circuit in the CAN bus
• Faulty CAN bus transceiver
• Corroded or loose ground connections
• Malfunctioning or incompatible aftermarket accessories
• Software issues or programming errors in the BCM
• Low battery voltage or power supply issues

Common misdiagnosis for U2644 Lost Communication with Body Control Module (BCM) – Bus Off.

• Faulty Body Control Module (BCM)
• Wiring issues or shorts in the communication lines
• Faulty or corroded connectors
• Issues with the CAN bus system
• Power supply problems to the BCM
• Faulty or malfunctioning sensors
• Other module communication failures
• Software or firmware issues in the BCM or other modules

Common Troubleshooting Steps

When dealing with the OBD-II code U2644, which indicates “Lost Communication with Body Control Module (BCM) – Bus Off,” 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 related to the BCM for any signs of damage, corrosion, or loose connections.
• **Connector Pins: Ensure that the pins in the connectors are not bent or corroded.
• 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.
• **Functionality: If possible, test the BCM in another vehicle or replace it with a known good unit to see if the problem persists.
• Check the CAN Bus System: **Bus Integrity: Inspect the CAN bus wiring for shorts, opens, or high resistance. Use a multimeter to check the resistance between the CAN High and CAN Low wires.
• **Termination Resistors: Ensure that the CAN bus has the correct termination resistors (typically 120 ohms) at both ends of the bus.
• Scan for Communication Issues: Use a scan tool to check if other modules on the CAN bus are communicating properly. If other modules are also showing communication issues, the problem may be with the bus itself rather than the BCM.
• Check for Interference: Look for any aftermarket devices or modifications that may interfere with the vehicle’s electrical system, such as alarms, remote starters, or stereo systems.
• Inspect Fuses: Check the fuses related to the BCM and the communication network. Replace any blown fuses and check if the issue persists.
• 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.
• Software Updates: Check if there are any software updates available for the BCM or other modules. Sometimes, manufacturers release updates to fix communication issues.
• Consult Technical Service Bulletins (TSBs): Look for any TSBs related to the specific make and model of the vehicle. Manufacturers may have documented common issues and fixes for the U2644 code.1
• Professional Diagnosis: If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership with advanced diagnostic tools. By following these steps, you should be able to identify the root cause of the U2644 code and take appropriate action to resolve the communication issue with the Body Control Module.