U1978 – Module Communication Failure

The ODBII code U1978 indicates a communication failure between modules in the vehicle’s network, suggesting that one or more control modules are not communicating properly with each other.

The severity of ODBII code U1978 is moderate.

Common Causes For: U1976 Lost Communication with the Hybrid Powertrain Control Module (HPCM) A.

• Faulty wiring or connectors
• Failed or malfunctioning control module
• Poor ground connections
• Intermittent communication issues
• Corroded or damaged pins in connectors
• Software or firmware issues
• Electrical interference
• Low battery voltage or power supply issues

Common misdiagnosis for U1978 U1978: “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

Common Troubleshooting Steps

The OBD-II code U1978 indicates a “Module Communication Failure,” which typically means that there is a problem with communication between various control modules in the vehicle. 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 wiring harnesses that connect the modules, as these can be prone to wear and tear.
• Check Power and Ground:
• Ensure that the affected module has a proper power supply and ground connection. Use a multimeter to check voltage and ground continuity.
• If the module is not receiving power or has a poor ground, it may not communicate properly.
• Test the Affected Module:
• If possible, test the affected module to ensure it is functioning correctly. This may involve bench testing or swapping with a known good module.
• If the module is faulty, it may need to be repaired or replaced.
• Inspect the CAN Bus:
• The communication between modules often occurs over a Controller Area Network (CAN) bus. Check for any issues with the CAN bus wiring, such as shorts or opens.
• Use a CAN bus scanner to monitor the communication and check for any abnormalities.
• Check for Software Updates:
• Sometimes, communication issues can be resolved with a software update. Check with the vehicle manufacturer for any available updates for the affected modules.
• 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 Service Manual:
• Refer to the vehicle’s service manual for specific diagnostic procedures related to the U1978 code and the modules involved.
• Professional Diagnosis:
• If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership with experience in diagnosing module communication issues. By following these steps, you should be able to identify and resolve the underlying cause of the U1978 code.