U1909 – BCM Communication Failure

The ODBII code U1909 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 U1909: “BCM Communication Failure” is generally considered moderate to severe.

Common Causes For: U1907 U1907: BCM Communication Failure

• Faulty Body Control Module (BCM)
• Damaged wiring or connectors
• Poor ground connections
• Corroded terminals
• Software issues or programming errors
• Malfunctioning CAN bus
• Interference from aftermarket accessories
• Low battery voltage or weak battery
• Faulty or damaged sensors connected to the BCM

Common misdiagnosis for U1909 U1909: “BCM Communication Failure”

• Faulty Body Control Module (BCM)
• Wiring issues or shorts in the communication lines
• Defective or corroded connectors
• Malfunctioning other control modules (e.g., PCM, ECM)
• Battery or power supply issues
• Software or firmware glitches
• Grounding problems
• Faulty sensors or actuators related to the BCM

Common Troubleshooting Steps

The OBD-II code U1909 indicates a “BCM Communication Failure,” which typically means 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 context and help identify the root cause of the communication failure.
• Inspect Wiring and Connectors: Visually inspect the wiring and connectors related to the BCM. Look for signs of damage, corrosion, or loose connections. Pay special attention to the ground connections, as poor grounding can lead to communication issues.
• Check Power Supply: Ensure that the BCM is receiving the correct voltage. Use a multimeter to check the power supply to the BCM. If the voltage is low or absent, trace the wiring back to the power source.
• Test the BCM: If possible, test the BCM to ensure it is functioning correctly. This may involve using specialized diagnostic equipment or swapping the BCM with a known good unit.
• Inspect Other Modules: Since the BCM communicates with other modules, check those modules for faults. Look for any signs of failure or communication issues in related systems (e.g., ABS, airbag, etc.).
• Check for Short Circuits: Use a multimeter to check for short circuits in the wiring harness connected to the BCM. A short circuit can disrupt communication between modules.
• Perform a Network Test: If you have access to a scan tool that can perform network tests, use it to check the communication between the BCM and other modules. This can help identify which module is causing the communication failure.
• Update Software/Firmware: Check if there are any software or firmware updates available for the BCM or other related modules. Sometimes, communication issues can be resolved with an update.
• Clear Codes and Test Drive: After performing any repairs or adjustments, clear the trouble codes and take the vehicle for a test drive to see if the U1909 code returns.
• Consult Service Manual: Refer to the vehicle’s service manual for specific diagnostic procedures and wiring diagrams related to the BCM and its communication network.1
• Seek Professional Help: If the issue persists after performing the above steps, consider seeking help from a professional mechanic or automotive technician who has experience with BCM-related issues. By following these troubleshooting steps, you should be able to identify and resolve the cause of the U1909 code.