U1986 – Module Communication Failure

The ODBII code U1986 indicates a “Module Communication Failure,” meaning there is a problem with communication between the vehicle’s control modules, which may affect their ability to share data or function properly.

The severity of ODBII code U1986 is moderate.

Common Causes For: U1985 U1985: “Module Communication Failure”

• Faulty wiring or connectors
• Failed or malfunctioning control module
• Corrupted software or firmware in the module
• Poor ground connections
• Interference from aftermarket devices
• Low battery voltage or power supply issues
• Communication network issues (e.g., CAN bus problems)

Common misdiagnosis for U1986 U1986: “Module Communication Failure”

• Faulty wiring or connectors
• Defective control modules
• Battery or power supply issues
• Software or firmware glitches
• Communication network problems (e.g., CAN bus issues)
• Grounding issues
• Intermittent faults in sensors or modules
• Incorrectly installed aftermarket accessories

Common Troubleshooting Steps

The OBD-II code U1986 indicates a “Module Communication Failure,” which typically means that there is a problem with communication 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 Power Supply: Ensure that the affected modules are receiving the proper voltage. Use a multimeter to check the power supply to the modules.
• Test Communication Lines:
• Use a scan tool to check the communication between modules. Some scan tools can perform a network test to see if modules are communicating properly.
• If you have access to a wiring diagram, check the communication lines (CAN bus, LIN bus, etc.) for continuity and shorts.
• Inspect the Modules:
• If you suspect a specific module is causing the issue, consider testing or replacing it.
• If possible, swap the suspected module with a known good one to see if the problem persists.
• Check for Software Updates: Sometimes, communication issues can be resolved with a software update. Check with the manufacturer for any available updates for the vehicle’s control modules.
• Clear Codes and Test Drive: After performing the above checks and repairs, clear the trouble codes and take the vehicle for a test drive to see if the code reappears.
• Consult Technical Service Bulletins (TSBs): Check for any TSBs related to the specific make and model of the vehicle. Manufacturers may have issued guidance on common communication issues.
• Professional Diagnosis: If the issue persists after performing the above steps, it may be necessary to consult a professional mechanic or dealership for further diagnosis. They may have specialized tools and knowledge to address complex communication issues. By following these steps, you can systematically identify and resolve the underlying cause of the U1986 code.