U1521 – Control Module Communication Failure

The ODBII code U1521 indicates a communication failure between control modules in a vehicle, suggesting that one or more modules are not properly communicating with each other.

Moderate to severe.

Common Causes For: U1520 U1520: Body Control Module Communication Error

• Faulty control module
• Damaged wiring or connectors
• Poor ground connections
• Corrupted software or firmware
• Communication network issues (CAN bus problems)
• Intermittent electrical connections
• Low battery voltage or power supply issues
• Faulty sensors or actuators affecting communication

Common misdiagnosis for U1521 U1521: Control Module Communication Failure

• Faulty control module
• Wiring issues or shorts
• Poor ground connections
• Corrupted software or firmware
• Faulty sensors
• Communication network issues (CAN bus problems)
• Battery or power supply issues
• Intermittent connection problems

Common Troubleshooting Steps

The OBD-II code U1521 indicates a “Control Module Communication Failure.” This code typically means that there is a communication issue between the vehicle’s control modules. Here are some common troubleshooting steps to diagnose and resolve the issue:

• Check for Additional 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: **Visual Inspection: Check the wiring and connectors related to the control modules for any signs of damage, corrosion, or loose connections.
• **Repair or Replace: Repair any damaged wires or connectors and ensure that all connections are secure.
• Check Power and Ground: **Power Supply: Verify that the control module has the proper power supply. Use a multimeter to check voltage at the module’s power pins.
• **Ground Connections: Ensure that the ground connections are clean and secure. A poor ground can lead to communication issues.
• Inspect the Control Modules: **Module Functionality: If possible, test the control module in question to ensure it is functioning correctly. This may involve swapping it with a known good module.
• **Software Updates: Check if there are any software updates available for the control module. Sometimes, manufacturers release updates to fix communication issues.
• Check for Interference: **Aftermarket Accessories: If any aftermarket accessories have been installed, they may interfere with the communication between modules. Temporarily disconnect them to see if the issue resolves.
• **Signal Interference: Ensure that there are no sources of electromagnetic interference near the vehicle’s wiring.
• Perform a Network Test: Use a scan tool capable of performing a network test to check the communication between modules. This can help identify which module is not communicating properly.
• 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 returns.
• 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 issues related to U1521.
• Seek Professional Help: If the issue persists after performing these 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 troubleshooting steps, you can systematically identify and resolve the underlying cause of the U1521 code.