U1858 – Module Communication Failure

The ODBII code U1858: Module Communication Failure indicates that there is a communication issue between the vehicle’s control modules, preventing them from exchanging data properly.

The severity of ODBII code **U1858: Module Communication Failure** is generally considered moderate to severe.

Common Causes For: U1839: Module Communication Fault

• Faulty wiring or connectors
• Failed control module
• Corrupted software or firmware
• Poor ground connections
• Intermittent electrical issues
• Low battery voltage
• Communication network issues (e.g., CAN bus problems)
• Damaged or corroded pins in connectors
• Incompatible or aftermarket modules installed

Common misdiagnosis for U1858: Module Communication Failure

• Faulty wiring or connectors
• Defective control modules
• Battery or power supply issues
• Software or firmware glitches
• Intermittent communication issues
• Grounding problems
• Incorrectly configured or programmed modules
• Faulty sensors or actuators

Common Troubleshooting Steps

The OBD-II code **U1858: Module Communication Failure** indicates that there is a communication issue between the vehicle’s control modules. This can be caused by various factors, including wiring issues, faulty modules, or problems with the vehicle’s network. Here are some common troubleshooting steps to diagnose and resolve this 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 and help identify which module is having communication problems.
• 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 failures.
• Check the Modules:
• Identify which module is reporting the U1858 code. This may require consulting the vehicle’s service manual or wiring diagrams.
• If possible, test the module for proper operation. This may involve checking power and ground circuits or using a scan tool to communicate with the module.
• Test the Communication Network:
• Use a multimeter or an oscilloscope to check the communication lines (CAN bus, LIN bus, etc.) for proper voltage levels and signals.
• Look for short circuits, open circuits, or noise on the communication lines.
• Check for Intermittent Issues:
• Sometimes, communication failures can be intermittent. If the issue is not consistently reproducible, try to observe the conditions under which the failure occurs (e.g., temperature, vibration, etc.).
• Reset the Modules:
• Clear the trouble codes using the OBD-II scanner and see if the code returns. Sometimes, a temporary glitch can cause communication issues that may resolve after a reset.
• Update Software/Firmware:
• Check if there are any software updates available for the vehicle’s modules. Sometimes, communication issues can be resolved with a software update.
• Consult Technical Service Bulletins (TSBs):
• Look for any TSBs related to the U1858 code or communication issues for your specific vehicle make and model. Manufacturers may have specific fixes or recommendations.
• Professional Diagnosis:
• If the issue persists after performing the above steps, it may be necessary to seek help from a professional technician or dealership. They may have specialized tools and knowledge to diagnose complex communication issues. By following these steps, you can systematically identify and address the underlying cause of the U1858 code.