U1771 – TCM-ECM Communication Failure

The ODBII code U1771 indicates a communication failure between the Transmission Control Module (TCM) and the Engine Control Module (ECM), suggesting that these two components are unable to exchange data properly.

The severity of ODBII code U1771: TCM-ECM Communication Failure is generally considered moderate to severe.

Common Causes For: 1. U1609: ECM-BCM Communication Failure

• Faulty wiring or connectors between TCM and ECM
• Failed TCM (Transmission Control Module)
• Failed ECM (Engine Control Module)
• Corroded or damaged connectors
• Poor ground connections
• Software issues or incompatibility
• Electrical interference or noise
• Blown fuses related to TCM or ECM

Common misdiagnosis for 1. U1771: TCM-ECM Communication Failure

• Faulty Transmission Control Module (TCM)
• Faulty Engine Control Module (ECM)
• Wiring issues or damaged connectors
• Faulty sensors (e.g., speed sensors)
• Software issues or programming errors
• Battery or power supply problems
• Grounding issues
• Transmission fluid issues or low fluid levels

Common Troubleshooting Steps

When dealing with OBD-II code U1771, which indicates a communication failure between the Transmission Control Module (TCM) and the Engine Control Module (ECM), there are several common troubleshooting steps you can follow to diagnose and potentially resolve the issue:

• Check for Additional Codes: Use an OBD-II scanner to check for any other related trouble codes. This can provide more context and help identify if there are other issues affecting communication.
• Inspect Wiring and Connectors:
• Visually inspect the wiring harness and connectors between the TCM and ECM for any signs of damage, corrosion, or loose connections.
• Ensure that all connectors are securely plugged in and that there are no bent pins.
• Check for Short Circuits or Open Circuits:
• Use a multimeter to test the wiring for continuity and to check for any short circuits or open circuits that could be interrupting communication.
• Inspect Ground Connections:
• Ensure that the ground connections for both the TCM and ECM are secure and free of corrosion. Poor grounding can lead to communication issues.
• Check Power Supply:
• Verify that both the TCM and ECM are receiving the proper voltage. Use a multimeter to check the power supply to both modules.
• Look for Software Updates:
• Check if there are any software updates available for the TCM or ECM. Sometimes, manufacturers release updates to fix communication issues.
• Perform a Hard Reset:
• Disconnect the battery for a few minutes to reset the vehicle’s computer systems. Reconnect the battery and see if the code reappears.
• Inspect for Environmental Factors:
• Check for any environmental factors that could affect communication, such as water intrusion or excessive heat.
• Test the Modules:
• If possible, test the TCM and ECM individually to ensure they are functioning correctly. This may involve using specialized diagnostic tools or swapping with known good modules.
• Consult Technical Service Bulletins (TSBs):
• Look for any TSBs related to U1771 for your specific vehicle make and model. Manufacturers may have documented common issues and solutions. 1
• Professional Diagnosis:
• If the issue persists after performing the above steps, consider seeking help from a professional mechanic or dealership. They may have access to advanced diagnostic tools and resources. By following these steps, you can systematically diagnose and address the communication failure indicated by the U1771 code.