U1389 – Control Module Communication Bus Off.

The ODBII code U1389 indicates a communication issue where a control module is unable to communicate on the vehicle’s communication bus, often due to a fault in the module or wiring.

The severity of ODBII code U1389 is moderate to severe.

Common Causes For: U1388 U1388: “Module Communication Failure”

• Faulty control module
• Poor electrical connections
• Damaged wiring or connectors
• Faulty communication bus (CAN bus) components
• Software issues or programming errors
• Low battery voltage
• Interference from aftermarket devices
• Corroded terminals or connectors

Common misdiagnosis for U1389 Control Module Communication Bus Off.

• Faulty control module
• Wiring issues
• Poor ground connections
• Corrupted software/firmware
• Faulty sensors
• Battery or power supply issues
• Communication network problems
• Intermittent connection issues

Common Troubleshooting Steps

The OBD-II code U1389 indicates a communication issue on the control module communication bus, specifically that a module is “off” or not responding. This can be caused by various factors, including wiring issues, module failures, or problems with the communication bus itself. Here are some common troubleshooting steps to diagnose and resolve the U1389 code:

• 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.
• Inspect Wiring and Connectors: Visually inspect the wiring and connectors related to the control modules. 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 the Control Modules: Identify the control module(s) that may be affected. This could include the engine control module (ECM), transmission control module (TCM), or other modules depending on the vehicle.
• If possible, test the affected module(s) for proper operation. This may involve using a scan tool to check for communication with the module.
• Test the Communication Bus: Use a multimeter or an oscilloscope to check the voltage levels and signal integrity on the communication bus (CAN bus, LIN bus, etc.).
• Look for short circuits, open circuits, or abnormal voltage levels that could indicate a problem.
• Check for Interference: Ensure that there are no aftermarket devices or modifications that could be interfering with the communication bus.
• Disconnect any non-factory accessories and see if the code persists.
• Perform a Hard Reset: Disconnect the vehicle’s battery for a few minutes to reset the control modules. Reconnect the battery and see if the code reappears.
• Update or Reprogram Modules: If the control module is not responding, it may need to be reprogrammed or updated with the latest software from the manufacturer.
• Replace Faulty Components: If a specific module is determined to be faulty after testing, it may need to be replaced.
• If wiring issues are found, repair or replace the damaged wiring or connectors.
• Consult Technical Service Bulletins (TSBs): Check for any TSBs related to the U1389 code for your specific vehicle make and model. Manufacturers may have known fixes or recommendations.
• Seek Professional Help: If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership with experience in diagnosing communication issues. By following these steps, you should be able to identify and resolve the underlying issue causing the U1389 code.