U1666 – Module Communication Failure

The ODBII code U1666 indicates a “Module Communication Failure,” meaning there is a problem with communication between the vehicle’s control modules.

The severity of ODBII code U1666 is generally considered moderate.

Common Causes For: U1665 Lost Communication with Body Control Module (BCM)”.

• Faulty wiring or connectors
• Malfunctioning control module
• Poor ground connections
• Intermittent communication issues
• Software or firmware issues
• Corroded terminals
• Electrical interference
• Low battery voltage or weak battery
• Faulty CAN bus system
• Damaged or shorted harnesses

Common misdiagnosis for U1666 U1666: “Module Communication Failure”

• Faulty wiring or connectors
• Defective control module
• Software issues or updates needed
• Battery or power supply problems
• Grounding issues
• Intermittent communication issues
• Other communication protocol failures

Common Troubleshooting Steps

The OBD-II code U1666 indicates a “Module Communication Failure,” which typically means that there is a problem with communication between the vehicle’s control modules. Here are some common troubleshooting steps to diagnose and resolve this issue:

• Check for Other Codes: Use an OBD-II scanner to check for any other trouble codes that may be present. Sometimes, multiple codes can provide more context for the issue.
• Inspect Wiring and Connectors:
• Visually inspect the wiring and connectors associated with the affected module(s). 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 affected module is receiving the proper voltage and ground. Use a multimeter to check the power supply to the module.
• Test the Module: If possible, test the affected module to ensure it is functioning correctly. This may involve using specialized diagnostic tools or swapping the module with a known good one.
• Check for Short Circuits: Use a multimeter to check for short circuits in the wiring harness. A short can disrupt communication between modules.
• Inspect the CAN Bus: If the vehicle uses a Controller Area Network (CAN) bus for communication, check the integrity of the CAN bus wiring. Look for any breaks or shorts in the bus lines.
• Look for Interference: Sometimes, aftermarket accessories or modifications can interfere with module communication. If any recent changes have been made to the vehicle, consider reverting them to see if the issue resolves.
• Perform a Network Test: Some advanced scan tools can perform a network test to check the communication between modules. This can help identify which module is not communicating properly.
• Update Software/Firmware: Check if there are any software or firmware updates available for the vehicle’s 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 code returns. 1
• Consult Technical Service Bulletins (TSBs): Check for any TSBs related to the U1666 code for your specific vehicle make and model. Manufacturers may have issued guidance on common issues and fixes. 1
• Seek Professional Help: If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or technician who has experience with your vehicle’s specific systems. By following these steps, you can systematically diagnose and potentially resolve the U1666 code and its underlying communication issues.