U1777 – Module Communication Fault

The ODBII code U1777 indicates a “Module Communication Fault,” which means there is a communication issue between the vehicle’s control modules.

The severity of ODBII code U1777 is generally considered moderate.

Common Causes For: U1776 U1776: Transmission Control Module Communication Error

• Faulty wiring or connectors
• Failed control module
• Corrupted software or firmware
• Poor ground connections
• Intermittent electrical issues
• Communication network faults (e.g., CAN bus issues)
• Low battery voltage or power supply issues
• Damaged or shorted sensors or actuators

Common misdiagnosis for U1777 U1777: “Module Communication Fault”

• Faulty wiring or connectors
• Defective control module
• Software issues or outdated firmware
• Battery or power supply problems
• Grounding issues
• Intermittent communication faults
• Other communication protocol errors

Common Troubleshooting Steps

The OBD-II code U1777 indicates a “Module Communication Fault,” which typically means that there is a communication issue between the vehicle’s control modules. 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 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 for Module Power Supply:
• Ensure that the affected modules are receiving the proper voltage and ground. Use a multimeter to check the power supply to the modules.
• If a module is not powered, trace the wiring back to the fuse box and check for blown fuses or damaged wiring.
• Test Communication Lines:
• Use a scan tool to check the communication lines (CAN bus, LIN bus, etc.) for continuity and proper signal levels.
• If you have access to an oscilloscope, you can check the waveform of the communication signals to ensure they are within specifications.
• Check for Intermittent Issues:
• Sometimes, communication faults can be intermittent. If the issue is not present during testing, consider monitoring the vehicle for a longer period to see if the fault reoccurs.
• Inspect Modules:
• If you suspect a specific module is causing the issue, consider testing or replacing it. Modules can fail and cause communication faults.
• If possible, swap the suspected module with a known good one to see if the problem resolves.
• Update Software/Firmware:
• Check if there are any software updates available for the vehicle’s control modules. Sometimes, communication issues can be resolved with a software update.
• Clear Codes and Test Drive:
• After performing any repairs or inspections, 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 related to the U1777 code and the modules involved.
• Seek Professional Help:
• If you are unable to resolve the issue after following these steps, consider seeking help from a professional mechanic or dealership with experience in diagnosing communication faults. By following these steps, you should be able to identify and resolve the underlying issue causing the U1777 code.