U1779 – Control Module Communication Bus Off.

The ODBII code U1779 indicates a communication issue where a control module is not able to communicate on the vehicle’s communication bus, often due to a fault in the module or wiring.

The severity of ODBII code U1779 is moderate to severe.

Common Causes For: U1777 U1777: “Module Communication Fault”

• Faulty control module
• Damaged wiring or connectors
• Poor ground connections
• Communication bus short circuit
• Open circuit in the communication bus
• Corroded connectors
• Intermittent electrical issues
• Software or firmware issues in the control module
• Low battery voltage or power supply issues
• Faulty or incompatible aftermarket components

Common misdiagnosis for U1779 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 U1779 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 software problems. Here are some common troubleshooting steps to diagnose and resolve the U1779 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 on the communication bus. 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 Power Supply: Ensure that the affected control module(s) are receiving the proper voltage. Use a multimeter to check the power supply to the module.
• Verify that the fuses related to the control modules are intact.
• Test the Control Module: If possible, perform a functional test of the control module that is reporting the U1779 code. This may involve using specialized diagnostic tools or software.
• If the module is not responding, it may need to be replaced or reprogrammed.
• Check for Short Circuits or Open Circuits: Use a multimeter to check for short circuits or open circuits in the communication lines (CAN bus, LIN bus, etc.).
• Inspect the bus lines for any signs of damage or interference.
• Look for Interference from Other Modules: Sometimes, other modules on the bus can cause communication issues. Disconnect other modules one at a time to see if the problem resolves.
• Update Software/Firmware: Check if there are any software or firmware updates available for the control modules. Sometimes, communication issues can be resolved with an update.
• Perform a Hard Reset: Disconnect the vehicle’s battery for a few minutes to reset the control modules. Reconnect and see if the code reappears.
• Consult Technical Service Bulletins (TSBs): Look for any TSBs related to the specific make and model of the vehicle. Manufacturers may have issued guidance on common issues related to U1779.
• Seek Professional Help: If the issue persists after performing the above steps, it may be necessary to consult a professional mechanic or technician who has experience with the specific vehicle and its systems. By following these troubleshooting steps, you can systematically identify and resolve the underlying cause of the U1779 code.