U1390 – Lost Communication with the Body Control Module (BCM).

The ODBII code U1390 indicates that there is a loss of communication between the vehicle’s control module and the Body Control Module (BCM), which may affect various electrical systems and functions.

The severity of ODBII code U1390 is generally considered moderate to severe.

Common Causes For: U1389 Control Module Communication Bus Off.

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

Common misdiagnosis for U1390 Lost Communication with the 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 sensors or actuators
• Battery or charging system problems
• Faulty ignition switch
• Software or firmware issues in the BCM or other modules

Common Troubleshooting Steps

When dealing with OBD-II code U1390, which indicates “Lost Communication with the 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 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.
• Check Power and Ground: **Power Supply: Verify that the BCM is receiving the correct voltage. Use a multimeter to check the power supply to the BCM.
• **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.
• Check for Communication Issues: **CAN Bus: Inspect the CAN bus wiring for shorts, opens, or other issues. The BCM communicates with other modules via the CAN bus, so any issues here can lead to communication loss.
• **Scan Other Modules: Use a scan tool to check if other modules can communicate with the BCM. If they cannot, the issue may be with the CAN bus or the BCM itself.
• Test the BCM: If possible, test the BCM in another vehicle (if you have access to one) to determine if the module itself is faulty.
• Alternatively, you can try replacing the BCM with a known good unit.
• Check for Software Updates: Check if there are any software updates available for the BCM or the vehicle’s control modules. Sometimes, manufacturers release updates to fix communication issues.
• Clear Codes and Test Drive: After performing the above checks and repairs, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns.
• Consult Technical Service Bulletins (TSBs): Look for any TSBs related to the specific make and model of the vehicle. Manufacturers may have issued bulletins regarding known issues with the BCM or communication problems.
• Seek Professional Help: If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or an automotive electrician who has experience with BCM issues. By following these steps, you should be able to identify and resolve the cause of the U1390 code. Always ensure safety and proper procedures when working on vehicle electronics.