U1790 – refers to a communication issue between the engine control module (ECM) and the transmission control module (TCM).

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The ODBII code U1790 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 U1790 is typically considered moderate to high.

Common Causes For: U1789 refers to a communication issue related to the transmission control module (TCM) in a vehicle.

  • Faulty wiring or connectors between ECM and TCM
  • Failed ECM or TCM
  • Corrupted software or firmware in ECM or TCM
  • Poor ground connections
  • Electrical interference or noise
  • Blown fuses related to ECM or TCM
  • Faulty sensors affecting communication
  • Issues with the vehicle’s CAN bus system

Common misdiagnosis for U1790 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)
  • Transmission fluid issues
  • Battery or charging system problems
  • Software or firmware issues
  • Grounding issues
  • Faulty CAN bus communication components

Common Troubleshooting Steps

When dealing with OBD-II code U1790, 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:

  • Check for Additional Codes: Use an OBD-II scanner to check for any other trouble codes that may be present. This can provide more context and help identify related issues.
  • 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 the wiring for continuity and to check 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 correct voltage. Use a multimeter to check the power supply to both modules.
  • Look for Software Updates:
  • Check if there are any available software updates 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.
  • Inspect for Interference:
  • Check for any aftermarket accessories or modifications that may be interfering with the communication between the ECM and TCM.
  • Test the Modules:
  • If all else fails, you may need to test the ECM and TCM individually to determine if one of the modules is faulty. This may require specialized diagnostic equipment.
  • Consult Technical Service Bulletins (TSBs):
  • Look for any TSBs related to the specific make and model of the vehicle, as they may provide additional guidance on resolving U1790. 1
  • Seek Professional Help:
  • If you are unable to resolve the issue after performing these steps, it may be best to consult a professional mechanic or technician who has experience with your vehicle’s specific systems. By following these troubleshooting steps, you can systematically identify and address the communication issue indicated by the U1790 code.

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