U2339 – Control Module Communication Bus Off.

The ODBII code U2339 indicates a communication issue where a control module is unable to communicate over the vehicle’s communication bus, often due to a fault in the module or wiring.

The severity of ODBII code U2339 is moderate to severe.

Common Causes For: U2337 U2337: “CAN Bus Communication Failure”

• Faulty control module
• Damaged wiring or connectors
• Poor ground connections
• Communication bus short circuit
• Open circuit in the communication bus
• Corroded connectors
• Software issues or bugs in the control module
• Interference from aftermarket devices
• Low battery voltage or power supply issues
• Faulty sensors or actuators on the bus

Common misdiagnosis for U2339 Control Module Communication Bus Off.

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

Common Troubleshooting Steps

The OBD-II code U2339 indicates a communication issue on the control module communication bus, specifically that a module is “off” or not communicating properly. 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 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.
• Inspect Wiring and Connectors: Visually inspect the wiring and connectors related to the control modules on the communication bus. Look for signs of damage, corrosion, or loose connections.
• Pay special attention to the connectors for the modules that are part of the communication bus.
• Check Power and Ground: Ensure that the affected control module has proper power and ground. Use a multimeter to check voltage at the module’s power supply pins and ground continuity.
• Test the Communication Bus: Use a scan tool to monitor the communication on the bus. Check if other modules are communicating properly.
• If possible, use an oscilloscope to check the signal integrity on the communication lines (CAN, LIN, etc.).
• Disconnect Modules: If multiple modules are connected to the same bus, try disconnecting them one at a time to isolate the faulty module. This can help identify if a specific module is causing the communication failure.
• Check for Short Circuits: Inspect the communication lines for any short circuits to ground or to each other. This can disrupt communication and cause modules to go offline.
• Update or Reprogram Modules: In some cases, a software update or reprogramming of the affected control module may resolve communication issues. Check with the manufacturer for any available updates.
• Replace Faulty Modules: If a specific module is identified as faulty and is not responding after checking all connections and power, it may need to be replaced.
• Clear Codes and Test Drive: After performing repairs, clear the trouble codes and take the vehicle for a test drive to see if the code returns.
• Consult Service Manual: Refer to the vehicle’s service manual for specific diagnostic procedures and wiring diagrams related to the communication bus.1
• Seek Professional Help: If the issue persists after performing these 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 cause of the U2339 code.