U1791 – Communication Network Malfunction

The ODBII code U1791: Communication Network Malfunction indicates a failure in the communication between various control modules in the vehicle’s network, which can affect their ability to exchange information properly.

The severity of ODBII code U1791 is moderate.

Common Causes For: U1790 refers to a communication issue between the engine control module (ECM) and the transmission control module (TCM).

• Faulty wiring or connectors in the communication network.
• Malfunctioning control modules.
• Corrupted software or firmware in control modules.
• Poor ground connections.
• Interference from aftermarket devices.
• Low battery voltage or power supply issues.
• Damaged or shorted communication lines.

Common misdiagnosis for U1791 U1791: Communication Network Malfunction

• Faulty wiring or connectors
• Defective control modules
• Incorrectly programmed modules
• Issues with the CAN bus system
• Power supply problems
• Grounding issues
• Faulty sensors
• Software glitches in the vehicle’s computer system

Common Troubleshooting Steps

The OBD-II code U1791 indicates a communication network malfunction, which typically means that there is an issue with the communication between various modules in the vehicle’s network. Here are some common troubleshooting steps to diagnose and resolve the U1791 code:

• Check for Other Codes: Use an OBD-II scanner to check for any additional trouble codes. Sometimes, other codes can provide more context about the issue.
• Inspect Wiring and Connectors:
• Visually inspect the wiring and connectors related to the communication network. Look for damaged, corroded, or loose connections.
• Pay special attention to the CAN (Controller Area Network) bus wiring, as this is often where communication issues arise.
• Check for Short Circuits or Open Circuits:
• Use a multimeter to check for continuity in the communication lines. Look for any short circuits or open circuits that could disrupt communication.
• Test Modules:
• If you suspect a specific module (like the engine control module, transmission control module, etc.) is causing the issue, you can test it by disconnecting it and checking if the code persists.
• If possible, swap the suspected module with a known good one to see if the problem resolves.
• Inspect the CAN Bus:
• Use a scan tool that can read live data to monitor the CAN bus. Check for any irregularities in the data being transmitted.
• Look for any modules that are not responding or are showing unusual behavior.
• Check Power and Ground:
• Ensure that all modules have proper power and ground connections. A weak ground or insufficient power can lead to communication issues.
• Update Software/Firmware:
• Check if there are any software or firmware updates available for the vehicle’s modules. Sometimes, updating the software can resolve communication issues.
• Clear Codes and Test Drive:
• After performing any repairs or adjustments, 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 U1791 code. Different manufacturers may have unique troubleshooting steps.
• 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 issue causing the U1791 code.