U1985 – Module Communication Failure

The ODBII code U1985 indicates a “Module Communication Failure,” meaning there is a problem with communication between vehicle control modules, which may affect their ability to share data or function properly.

The severity of ODBII code U1985 is moderate.

Common Causes For: U1984 U1984: “Module Communication Failure”

• Faulty wiring or connectors
• Malfunctioning control module
• Poor ground connections
• Corrupted software or firmware
• Intermittent electrical issues
• Low battery voltage
• Communication network issues (e.g., CAN bus problems)
• Incompatible or missing modules

Common misdiagnosis for U1985 U1985: “Module Communication Failure”

• Faulty wiring or connectors
• Defective control module
• Software issues or updates needed
• Battery or power supply problems
• Grounding issues
• Intermittent communication issues
• Other communication protocol failures
• Sensor malfunctions

Common Troubleshooting Steps

The OBD-II code U1985 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 if you can communicate with the affected module. If you cannot, it may indicate a problem with the module itself or the communication lines.
• If possible, use an oscilloscope to check the data lines for proper signals.
• Inspect the CAN Bus: If your vehicle uses a Controller Area Network (CAN) bus for communication, check for issues on the bus:
• Look for short circuits or open circuits in the CAN wiring.
• Check for termination resistors at both ends of the CAN bus; they should be present and functioning correctly.
• Check for Module Malfunction: If the wiring and connections are good, the issue may lie with the module itself. Consider:
• Testing the module in another vehicle (if possible) to see if it functions correctly.
• Replacing the module if it is determined to be faulty.
• Software Updates: Check if there are any software updates available for the vehicle’s modules. Sometimes, communication issues can be resolved with a software update.
• Clear Codes and Test Drive: After performing the above checks and repairs, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to 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 communication issues.
• Seek Professional Help: If the problem persists after performing these 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 U1985 code.