U2120 – BCM Communication Failure

The ODBII code U2120 indicates a communication failure between the Body Control Module (BCM) and other modules in the vehicle’s network, suggesting a disruption in data exchange.

The severity of ODBII code U2120: “BCM Communication Failure” is generally considered moderate to severe.

Common Causes For: U2119 Lost Communication with the Transmission Control Module (TCM).

• Faulty Body Control Module (BCM)
• Damaged wiring or connectors
• Poor ground connections
• Corroded terminals
• Software issues or programming errors
• Malfunctioning communication network (CAN bus)
• Other module failures affecting communication
• Battery voltage issues

Common misdiagnosis for U2120 U2120: “BCM Communication Failure”

• Faulty Body Control Module (BCM)
• Wiring issues or shorts in the communication lines
• Faulty or corroded connectors
• Issues with other control modules (e.g., PCM, ECM)
• Software or firmware issues in the BCM
• Battery or power supply problems
• Grounding issues
• Faulty sensors or actuators related to the BCM
• Intermittent communication issues due to environmental factors
• Incorrectly configured aftermarket accessories or modifications

Common Troubleshooting Steps

The OBD-II code U2120 indicates a “BCM Communication Failure,” which 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 additional context for the issue.
• Inspect 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.
• 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 or replace it with a known good unit to see if the problem persists.
• Check Communication Lines: **CAN Bus: If your vehicle uses a CAN bus system, check the communication lines for continuity and proper voltage levels. Look for shorts or open circuits.
• **Scope Testing: Use an oscilloscope to check the data lines for proper signal patterns.
• Inspect Other Modules: Since the BCM communicates with other modules, check those modules for faults. Look for codes or issues in related systems (e.g., lighting, security, etc.).
• Check for Software Updates: Sometimes, a software update for the BCM or other modules can resolve communication issues. Check with the manufacturer for any available updates.
• Clear Codes and Test Drive: After performing checks and repairs, clear the codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns.
• Consult Service Manual: Refer to the vehicle’s service manual for specific diagnostic procedures related to the BCM and communication issues.
• Professional Diagnosis: If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership with advanced diagnostic tools.Conclusion Troubleshooting a U2120 code can involve a combination of visual inspections, electrical testing, and module checks. It’s important to approach the diagnosis methodically to identify the root cause of the communication failure.