U1904 – BCM Communication Failure

The ODBII code U1904 indicates a communication failure between the Body Control Module (BCM) and other modules in the vehicle’s network, suggesting a problem with data exchange or connectivity.

The severity of ODBII code U1904: “BCM Communication Failure” is moderate.

Common Causes For: U1903 U1903: Instrument Cluster CAN Communication Fault

• Faulty Body Control Module (BCM)
• Damaged wiring or connectors
• Poor ground connections
• Corroded terminals
• Communication network issues (CAN bus problems)
• Software glitches or outdated firmware
• Malfunctioning related modules (e.g., PCM, ABS)
• Battery voltage issues or low power supply

Common misdiagnosis for U1904 U1904: “BCM Communication Failure”

• Faulty Body Control Module (BCM)
• Wiring issues or shorts in the communication lines
• Defective or corroded connectors
• Malfunctioning Instrument Cluster
• Issues with the Powertrain Control Module (PCM)
• Problems with the Anti-lock Braking System (ABS) module
• Faulty or weak battery
• Software glitches or programming errors in the BCM or other modules

Common Troubleshooting Steps

The OBD-II code U1904 indicates a “BCM Communication Failure,” which typically means that there is a problem with the communication between the Body Control Module (BCM) and other modules in the vehicle. Here are some common troubleshooting steps to diagnose and resolve this issue:

• Check for Additional Codes: Use an OBD-II scanner to check for any other trouble codes that may be present. Other codes can provide additional context for the issue.
• Inspect Wiring and Connectors: **Visual Inspection: Check the wiring harnesses 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.
• **Module Functionality: If possible, test the BCM in another vehicle to confirm it is functioning correctly.
• Check Communication Lines: **CAN Bus: If your vehicle uses a CAN (Controller Area Network) bus, check the communication lines for continuity and resistance. Look for shorts or open circuits.
• **Scope Testing: Use an oscilloscope to check the data signals on the CAN bus for proper communication.
• Inspect Other Modules: Since the BCM communicates with other modules, check those modules for faults. Look for codes or issues in related modules (e.g., PCM, ABS, etc.).
• Battery and Ground Connections: Ensure that the vehicle’s battery is in good condition and that all ground connections are clean and secure. A weak battery or poor ground can cause communication issues.
• Software Updates: Check if there are any software updates available for the BCM or other modules. Sometimes, manufacturers release updates to fix communication issues.
• Reset the System: After performing checks and repairs, clear the codes using the OBD-II scanner and see if the code returns after a test drive.
• Professional Diagnosis: If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership. They may have specialized diagnostic tools and experience with your specific vehicle model.
• Replacement: If the BCM is determined to be faulty after all tests, it may need to be replaced. Ensure that any replacement BCM is programmed to your vehicle. By following these steps, you should be able to identify and resolve the cause of the U1904 code. Always refer to the vehicle’s service manual for specific procedures and specifications related to your make and model.