U1661 – Lost Communication with Body Control Module (BCM).

The ODBII code U1661 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.

The severity of ODBII code U1661 is generally considered moderate to severe.

Common Causes For: U1660 Lost Communication with Body Control Module (BCM).

• Faulty Body Control Module (BCM)
• Damaged wiring or connectors
• Poor ground connection
• Corroded terminals
• Faulty communication network (CAN bus)
• Blown fuses
• Software issues or programming errors
• Intermittent electrical issues

Common misdiagnosis for U1661 Lost Communication with 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 fuses
• Communication network issues (CAN bus problems)
• Grounding issues
• Faulty sensors or actuators
• Software or firmware issues in the BCM or other modules

Common Troubleshooting Steps

When dealing with the OBD-II code U1661, which indicates “Lost Communication with 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 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 Communication: Use a scan tool to check if the BCM is communicating with other modules on the CAN bus. If other modules are also not communicating, the issue may be with the bus itself.
• **Scope Testing: If available, use an oscilloscope to check the CAN bus signals for proper voltage levels and signal integrity.
• Check for Short Circuits: Inspect the wiring for any short circuits to ground or power that could affect communication with the BCM.
• Look for Environmental Factors: Consider if there have been any recent changes to the vehicle, such as aftermarket installations, that could affect the BCM or its communication.
• Reset the System: Clear the trouble codes using the OBD-II scanner and see if the code returns. Sometimes, a temporary glitch can cause communication issues.
• Consult Technical Service Bulletins (TSBs): Check for any TSBs related to the specific make and model of the vehicle that may address known issues with the BCM or communication 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 root cause of the U1661 code and take appropriate action to resolve the communication issue with the Body Control Module.