U1774 – Transmission Control Module Communication Error

The ODBII code U1774 indicates a communication error between the Transmission Control Module (TCM) and other control modules in the vehicle, suggesting a possible issue with data transmission or connectivity.

Moderate to severe.

Common Causes For: U1773 U1773: Transmission Control Module Communication Error

• Faulty Transmission Control Module (TCM)
• Damaged wiring or connectors
• Poor electrical connections
• Faulty Engine Control Module (ECM)
• Software issues or bugs
• Low battery voltage
• Corroded terminals
• Faulty CAN bus communication
• Intermittent electrical issues
• Grounding problems

Common misdiagnosis for U1774 U1774: Transmission Control Module Communication Error

• Faulty Transmission Control Module (TCM)
• Wiring issues or damaged connectors
• Faulty Engine Control Module (ECM)
• Low transmission fluid levels
• Faulty sensors (e.g., speed sensors)
• Software issues or outdated firmware
• Battery or charging system problems
• Grounding issues
• Corroded or loose electrical connections
• Faulty CAN bus communication components

Common Troubleshooting Steps

The OBD-II code U1774 indicates a communication error between the Transmission Control Module (TCM) and other modules in the vehicle’s network. 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 additional trouble codes. Sometimes, related codes can provide more context for the issue.
• Inspect Wiring and Connectors:
• Visually inspect the wiring harness and connectors associated with the TCM. Look for signs of damage, corrosion, or loose connections.
• Ensure that all connectors are securely plugged in and that there are no bent pins.
• Check Power and Ground:
• Verify that the TCM is receiving the correct voltage and ground. Use a multimeter to check the power supply and ground connections to the TCM.
• If there is no power or ground, trace the wiring back to the source to identify any breaks or shorts.
• Test the TCM:
• If the wiring and connections are intact, the TCM itself may be faulty. Testing the TCM may require specialized equipment or a professional diagnostic tool.
• In some cases, reprogramming or updating the TCM software may resolve communication issues.
• Inspect the CAN Bus:
• The TCM communicates with other modules via the Controller Area Network (CAN) bus. Check for any issues with the CAN bus wiring or connections.
• Use a scan tool to monitor the CAN bus for any irregularities or communication failures.
• Check for Interference:
• Look for any aftermarket devices or modifications that may interfere with the vehicle’s communication network. This includes alarm systems, stereo systems, or other electronic devices.
• 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 U1774 code for your specific vehicle make and model. Manufacturers may have issued guidance on common issues and fixes.
• Seek Professional Help:
• If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or technician who has experience with transmission control systems and can perform more advanced diagnostics. By following these steps, you can systematically identify and address the underlying cause of the U1774 code.