U1256 – Control Module Communication Failure

The ODBII code U1256 indicates a “Control Module Communication Failure,” meaning there is a problem with communication between the vehicle’s control modules, which can affect various systems and functions.

The severity of ODBII code U1256 is moderate to high.

Common Causes For: U1255 SCP (J1850) Invalid or Missing Data for Network Control

• Faulty control module
• Poor electrical connections
• Damaged wiring harness
• Corroded connectors
• Software issues or bugs
• Low battery voltage
• Faulty or disconnected sensors
• Interference from aftermarket devices
• Grounding issues
• Communication network failure (e.g., CAN bus issues)

Common misdiagnosis for U1256 U1256: “Control Module Communication Failure”

• Faulty control module
• Wiring issues
• Poor ground connections
• Corrupted software/firmware
• Faulty sensors
• Battery or charging system problems
• Intermittent connection issues
• Communication network faults (CAN bus issues)

Common Troubleshooting Steps

The OBD-II code U1256 indicates a “Control Module Communication Failure.” This code 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, U1256 can be accompanied by other codes that can provide additional context for the issue.
• Inspect Wiring and Connectors:
• Visually inspect the wiring and connectors associated with the control modules. Look for signs of damage, corrosion, or loose connections.
• Pay special attention to the wiring harnesses that connect the modules, as these can be prone to wear and tear.
• Check Power and Ground:
• Ensure that the control modules have proper power and ground connections. Use a multimeter to check for voltage at the module connectors.
• Verify that the ground connections are clean and secure.
• Test Control Modules:
• If you suspect a specific control module is causing the issue, you can test it by swapping it with a known good module (if available) or by using a diagnostic tool to check its functionality.
• Some modules may have self-diagnostic capabilities that can provide more information.
• Inspect the CAN Bus:
• The communication between control modules often occurs over a Controller Area Network (CAN) bus. Check the integrity of the CAN bus wiring and connections.
• Use an oscilloscope or a CAN bus diagnostic tool to monitor the bus for proper communication signals.
• Check for Interference:
• Look for any aftermarket devices or modifications that may interfere with the communication between modules, such as alarm systems, stereo systems, or other electronic accessories.
• Clear Codes and Test Drive:
• After performing inspections 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 Service Manual:
• Refer to the vehicle’s service manual for specific diagnostic procedures related to the U1256 code. This may include specific tests or procedures for your vehicle make and model.
• Professional Diagnosis:
• If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership. They may have specialized diagnostic tools and experience to pinpoint the problem. By following these steps, you should be able to identify and resolve the underlying issue causing the U1256 code.