U1981 – Lost Communication with the Body Control Module (BCM).

The ODBII code U1981 indicates that there is a lost communication issue 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 U1981 is generally considered moderate to high.

Common Causes For: U1980 Lost Communication with the Body Control Module (BCM).

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

Common misdiagnosis for U1981 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 Instrument Cluster
• Battery or charging system problems
• Faulty fuses related to the BCM
• Software or firmware issues in the BCM
• Grounding issues in the electrical system
• Other module communication failures (e.g., ABS, HVAC)

Common Troubleshooting Steps

When dealing with OBD-II code U1981, 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 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: If your vehicle uses a CAN bus system, check the communication lines for continuity and proper voltage levels.
• **Scan Tool: Use a scan tool to see if you can communicate with the BCM. If you can’t, it may indicate a problem with the BCM itself or the communication lines.
• Check for Intermittent Issues: **Temperature Sensitivity: Sometimes, issues can be temperature-related. Check if the problem occurs only under certain conditions (e.g., when the vehicle is hot or cold).
• **Vibration: Check if the issue occurs when the vehicle is in motion or over bumps.
• Look for Related Modules: **Other Modules: Check if other modules (like the PCM, ABS, etc.) are communicating properly. A failure in one module can sometimes affect communication with the BCM.
• 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.
• Consult Technical Service Bulletins (TSBs): Check for any TSBs related to the BCM or communication issues for your specific vehicle make and model. Manufacturers may have known fixes for common problems.
• 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 U1981 code and take appropriate action to resolve it.