U1989 – Module Communication Failure

The ODBII code U1989: Module Communication Failure indicates that there is a communication issue between the vehicle’s control modules, preventing them from exchanging data properly.

The severity of ODBII code **U1989: Module Communication Failure** is generally considered moderate to severe, depending on the specific vehicle and the affected systems.

Common Causes For: U1977: Module Communication Fault

• Faulty wiring or connectors
• Failed control module
• Corrupted software or firmware
• Poor ground connections
• Interference from aftermarket devices
• Low battery voltage
• Communication network issues (e.g., CAN bus problems)
• Damaged or corroded pins in connectors
• Incompatible modules installed
• Faulty or damaged sensors

Common misdiagnosis for U1989: Module Communication Failure

• Faulty wiring or connectors
• Defective control module
• Software issues or outdated firmware
• Power supply problems
• Grounding issues
• Intermittent communication issues
• Other communication protocol failures
• Sensor malfunctions
• Battery or charging system problems
• Environmental interference

Common Troubleshooting Steps

The OBD-II code **U1989: Module Communication Failure** indicates that there is a communication issue between the vehicle’s control modules. This can be caused by various factors, including wiring issues, faulty modules, or problems with the vehicle’s network. 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 failures.
• Check the Module:
• If a specific module is indicated in the code or if you suspect a particular module, check its functionality. This may involve testing the module with a scan tool or replacing it if necessary.
• Ensure that the module is properly powered and that all necessary fuses are intact.
• Verify Network Communication:
• Use a scan tool to check the communication between modules. Some advanced scan tools can display live data and show if certain modules are responding.
• If possible, perform a network test to ensure that all modules are communicating correctly.
• Inspect the CAN Bus:
• If your vehicle uses a Controller Area Network (CAN) bus, check for issues with the bus itself. Look for shorts, opens, or other faults in the wiring.
• You can use an oscilloscope to check the signal integrity on the CAN bus lines.
• Check for Software Updates:
• Sometimes, communication issues can be resolved with a software update for the affected module(s). Check with the manufacturer for any available updates.
• Reset the Modules:
• Disconnect the battery for a few minutes to reset the modules. Reconnect and see if the code reappears.
• After resetting, perform a drive cycle to see if the issue persists.
• Consult Technical Service Bulletins (TSBs):
• Check for any TSBs related to the U1989 code for your specific vehicle make and model. Manufacturers may have known fixes or recommendations for this issue.
• Professional Diagnosis:
• If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership. They may have specialized tools and knowledge to diagnose complex communication issues. By following these steps, you should be able to identify and resolve the underlying cause of the U1989 code.