U1397 – Communication Bus Off.

The ODBII code U1397 indicates a communication issue where the vehicle’s communication bus is offline or not functioning properly, affecting data exchange between modules.

The severity of ODBII code U1397 is moderate to severe.

Common Causes For: U1396 U1396: “Control Module Communication Failure”

• Faulty wiring or connectors in the communication bus.
• Malfunctioning control modules.
• Short circuits or open circuits in the communication lines.
• Poor ground connections.
• Interference from aftermarket devices.
• Software or firmware issues in the control modules.
• Low battery voltage or power supply issues.

Common misdiagnosis for U1397 Communication Bus Off.

• Faulty ABS module
• Defective engine control module (ECM)
• Malfunctioning transmission control module (TCM)
• Bad wiring or connectors
• Faulty body control module (BCM)
• Incorrectly diagnosed sensor issues
• Power supply problems
• Communication issues with other modules

Common Troubleshooting Steps

The OBD-II code U1397 indicates a “Communication Bus Off” issue, which typically means that there is a problem with the communication between the vehicle’s control modules. 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 U1397 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 communication bus (CAN bus). Look for signs of damage, corrosion, or loose connections.
• Pay special attention to the connectors at the control modules and any junction points.
• Test the Communication Bus: Use a multimeter or an oscilloscope to check the voltage levels on the CAN bus wires. The typical voltage should be around 2.5V to 2.7V when the vehicle is on.
• Check for short circuits or open circuits in the communication lines.
• Check Control Modules: Identify the control modules that are part of the communication network. This may include the engine control module (ECM), transmission control module (TCM), body control module (BCM), etc.
• If possible, perform a module scan to see if any specific module is not responding.
• Look for Ground Issues: Ensure that all ground connections for the control modules are secure and free of corrosion. Poor grounding can lead to communication issues.
• Inspect for Interference: Check for any aftermarket devices or modifications that may interfere with the communication bus, such as alarms, remote starters, or stereo systems.
• 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 returns.
• Update or Reprogram Modules: If a specific control module is identified as the issue, check if there are any software updates or reprogramming procedures available from the manufacturer.
• Replace Faulty Components: If a specific module is determined to be faulty after testing, it may need to be replaced.
• Consult Technical Service Bulletins (TSBs): Check for any TSBs related to the U1397 code for your specific vehicle make and model. Manufacturers may have known fixes or recommendations.1
• Seek Professional Help: If the issue persists after performing these steps, it may be best to consult a professional mechanic or technician who has experience with your vehicle’s specific systems. By following these troubleshooting steps, you should be able to identify and resolve the underlying issue causing the U1397 code.