U1940 – Lost Communication with the Body Control Module (BCM).

The ODBII code U1940 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 functions and systems in the vehicle.

The severity of ODBII code U1940 is generally considered moderate.

Common Causes For: U1939 U1939: CAN Bus Communication Fault

• 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 U1940 Lost Communication with the Body Control Module (BCM).

• Faulty Body Control Module (BCM)
• Wiring issues or damaged connectors
• Faulty Instrument Cluster
• Malfunctioning Powertrain Control Module (PCM)
• Battery or charging system problems
• Faulty ignition switch
• Corrupted software or firmware in the BCM
• Grounding issues
• Faulty CAN bus communication lines
• Other module communication failures

Common Troubleshooting Steps

When dealing with OBD-II code U1940, 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 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 and configured for the vehicle.
• Test Communication Lines: **CAN Bus: If your vehicle uses a CAN bus system, check the communication lines for continuity and proper signal. You may need an oscilloscope to check for data transmission.
• **Network Issues: Look for any other modules on the network that may be causing communication issues.
• Check for Short Circuits: Use a multimeter to check for short circuits in the wiring that connects the BCM to other modules.
• Inspect Related Modules: If other modules are involved in the communication network, check their functionality and connections as well. A fault in another module can sometimes cause communication issues 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 U1940 code for your specific vehicle make and model. Manufacturers may have issued guidance on common issues and fixes.
• Seek Professional Help: If the issue persists after performing the above steps, it may be necessary to consult a professional mechanic or dealership for further diagnosis. They may have specialized tools and knowledge to address complex communication issues.Conclusion Troubleshooting OBD-II code U1940 involves a systematic approach to check for wiring issues, power supply, module functionality, and communication integrity. Following these steps can help identify the root cause of the communication loss with the BCM.