U1797 – refers to a communication issue between the engine control module (ECM) and the transmission control module (TCM).

The ODBII code U1797 indicates a communication issue between the engine control module (ECM) and the transmission control module (TCM), suggesting a failure in data exchange between these two components.

The severity of ODBII code U1797 is typically considered moderate to severe.

Common Causes For: U1796 U1796: “Control Module Communication Failure”

• Faulty wiring or connectors between ECM and TCM
• Failed ECM or TCM
• Corrupted software or firmware in ECM or TCM
• Poor ground connections
• Short circuits or open circuits in the communication lines
• Interference from other electronic components
• Low battery voltage or weak battery
• Faulty CAN bus communication system

Common misdiagnosis for U1797 refers to a communication issue between the engine control module (ECM) and the transmission control module (TCM).

• Faulty ECM
• Faulty TCM
• Wiring issues or shorts
• Corroded connectors
• Faulty sensors (e.g., speed sensors)
• Software issues or updates needed
• Battery or charging system problems
• Transmission fluid issues
• Grounding problems
• Other communication errors in the vehicle’s network

Common Troubleshooting Steps

When dealing with OBD-II code U1797, which indicates a communication issue between the Engine Control Module (ECM) and the Transmission Control Module (TCM), 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 trouble codes that may be present. Sometimes, multiple codes can provide more context for the issue.
• Inspect Wiring and Connectors:
• Visually inspect the wiring harness and connectors between the ECM and TCM 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 for continuity in the wiring between the ECM and TCM. Look for any short circuits or open circuits that could be causing communication issues.
• Inspect Ground Connections:
• Ensure that the ground connections for both the ECM and TCM are secure and free of corrosion. Poor grounding can lead to communication problems.
• Check Power Supply:
• Verify that both the ECM and TCM 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 ECM or TCM. Sometimes, manufacturers release updates to fix communication issues.
• Perform a Hard Reset:
• Disconnect the battery for a few minutes to reset the ECM and TCM. Reconnect the battery and see if the code reappears.
• Test the Modules:
• If possible, test the ECM and TCM individually to ensure they are functioning correctly. This may require specialized diagnostic equipment.
• Check for Interference:
• Look for any aftermarket accessories or modifications that may be interfering with the communication between the ECM and TCM.
• Consult Technical Service Bulletins (TSBs):
• Check for any TSBs related to your vehicle’s make and model that may address known issues with ECM/TCM communication. 1
• 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 your specific vehicle make and model. By following these troubleshooting steps, you can systematically identify and address the underlying cause of the U1797 code.