U1839 – Module Communication Fault

The ODBII code U1839: Module Communication Fault indicates a communication issue between the vehicle’s control modules, suggesting that one or more modules are not properly communicating with each other.

The severity of ODBII code **U1839: Module Communication Fault** is generally considered moderate to severe.

Common Causes For: U1837: Control Module Communication Fault

• Faulty wiring or connectors
• Malfunctioning control modules
• Corrupted software or firmware in modules
• Poor ground connections
• Interference from aftermarket devices
• Low battery voltage or power supply issues
• Communication bus faults (e.g., CAN bus issues)

Common misdiagnosis for U1839: Module Communication Fault

• Faulty wiring or connectors
• Defective control module
• Power supply issues
• Software glitches or updates needed
• Intermittent communication issues
• Grounding problems
• Other communication protocol errors
• Sensor malfunctions

Common Troubleshooting Steps

The OBD-II code **U1839: Module Communication Fault** indicates a communication issue between modules in the vehicle’s network. This can be caused by various factors, including wiring issues, faulty modules, or problems with the vehicle’s communication protocols. 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. This can provide more context about the issue and help identify which module is having communication problems.
• Inspect Wiring and Connectors:
• Visually inspect the wiring and connectors associated with the affected modules. Look for signs of damage, corrosion, or loose connections.
• Pay special attention to the ground connections, as poor grounding can lead to communication faults.
• Check Module Power Supply: Ensure that the affected modules are receiving the proper voltage and ground. Use a multimeter to check the power supply at the module connectors.
• Test Communication Lines:
• Use a scan tool to monitor the communication lines (CAN bus, LIN bus, etc.) for activity.
• Check for short circuits or open circuits in the communication lines.
• Perform a Network Test: If available, use a specialized diagnostic tool to perform a network test. This can help identify which module is not communicating properly.
• Inspect for Water Intrusion: Check for any signs of water intrusion in the areas where the modules are located, as moisture can cause communication issues.
• Reset the Modules: Sometimes, resetting the modules can resolve temporary communication faults. Disconnect the battery for a few minutes, then reconnect it and see if the code returns.
• 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.
• Replace Faulty Modules: If a specific module is identified as faulty and is not responding to troubleshooting efforts, it may need to be replaced.
• Consult Service Manual: Refer to the vehicle’s service manual for specific diagnostic procedures related to the U1839 code and the modules involved. 1
• Professional Diagnosis: If the issue persists after performing these steps, consider seeking help from a professional mechanic or dealership with advanced diagnostic equipment. By following these steps, you can systematically identify and resolve the underlying cause of the U1839 code.