U1504 – Transmission Control Module Communication Error

The ODBII code U1504 indicates a communication error between the Transmission Control Module (TCM) and other control modules in the vehicle, suggesting a potential issue with data transmission or connectivity.

The severity of ODBII code U1504 is moderate to severe.

Common Causes For: U1503 U1503: CAN Bus Communication Fault

• Faulty Transmission Control Module (TCM)
• Damaged wiring or connectors
• Poor ground connections
• Corrupted software or firmware in the TCM
• Faulty Engine Control Module (ECM)
• Communication network issues (CAN bus problems)
• Low battery voltage or electrical issues
• Corroded terminals or connectors
• Malfunctioning sensors related to transmission
• Aftermarket modifications affecting communication systems

Common misdiagnosis for U1504 U1504: 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 transmission sensors (e.g., speed sensors)
• Corrupted software or firmware in the TCM
• Battery or charging system issues
• Grounding problems
• Faulty CAN bus communication
• Other transmission-related issues (e.g., solenoid problems)

Common Troubleshooting Steps

The OBD-II code U1504 indicates a communication error between the Transmission Control Module (TCM) and other 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 additional trouble codes. Sometimes, other codes can provide context or indicate related issues.
• 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 power supply. Use a multimeter to check the voltage at the TCM connector.
• Check the ground connections to ensure they are secure and free of corrosion.
• 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, such as shorts or opens.
• Use a scan tool to monitor the CAN bus for communication errors or abnormalities.
• Test the TCM:
• If the wiring and connections are good, the TCM itself may be faulty. If possible, test the TCM in another vehicle or replace it with a known good unit to see if the problem persists.
• Check for Software Updates:
• Sometimes, a software update for the TCM or other control modules can resolve communication issues. Check with the manufacturer for any available updates.
• Clear Codes and Test Drive:
• After performing any repairs or checks, 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 TCM and communication errors. This can provide additional insights and steps tailored to your vehicle 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 tools and knowledge to diagnose complex communication issues. By following these steps, you can systematically identify and address the cause of the U1504 code.