U1984 – Module Communication Failure

The ODBII code U1984 indicates a “Module Communication Failure,” meaning that there is a problem with communication between the vehicle’s control modules, which may affect their ability to share data or function properly.

The severity of ODBII code U1984 is moderate.

Common Causes For: U1983 Lost Communication with the Body Control Module (BCM)”.

• Faulty wiring or connectors
• Failed or malfunctioning control module
• Poor ground connections
• Corroded or damaged pins in connectors
• Communication network issues (e.g., CAN bus problems)
• Software or firmware issues in modules
• Intermittent electrical connections
• Low battery voltage or power supply issues

Common misdiagnosis for U1984 U1984: “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 U1984 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.
• If the module is not receiving power, trace the wiring back to the fuse box and check for blown fuses or damaged wires.
• Test the Module:
• If possible, test the affected module by swapping it with a known good module (if applicable) to see if the problem persists.
• Some modules may have self-diagnostic capabilities; consult the service manual for specific testing procedures.
• Check for Communication:
• Use a scan tool to check if you can communicate with the affected module. If you cannot, it may indicate a problem with the module itself or the communication network.
• Check the communication lines (CAN bus, LIN bus, etc.) for continuity and proper signal levels.
• Inspect the CAN Bus:
• If the vehicle uses a CAN bus system, check for any short circuits or open circuits in the bus wiring.
• Use an oscilloscope to monitor the CAN bus signals if you have access to one, as this can help identify communication issues.
• Look for Intermittent Issues:
• Sometimes, communication failures can be intermittent. Pay attention to when the code appears (e.g., during specific driving conditions) and look for patterns.
• 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 checks, clear the trouble codes and take the vehicle for a test drive to see if the code returns.
• Consult Technical Service Bulletins (TSBs):
• Check for any TSBs related to the specific make and model of the vehicle. Manufacturers may have issued guidance on known communication issues. 1
• Seek Professional Help:
• If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or dealership for further diagnosis. By following these steps, you can systematically identify and resolve the underlying cause of the U1984 code.