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U code network Medium severity

U1794 SCP (J1850) Lack of Acknowledgment for Mirrors

The OBD2 code U1794 SCP (J1850) indicates a communication issue where the vehicle's control module is not receiving an acknowledgment signal from the mirrors' control module, suggesting a potential fault in the wiring,...

Definition

The OBD2 code U1794 SCP (J1850) indicates a communication issue where the vehicle's control module is not receiving an acknowledgment signal from the mirrors' control module, suggesting a potential fault in the wiring, connectors, or the mirrors' control module itself

Common causes

  • Faulty mirror control module
  • Damaged wiring or connectors
  • Poor ground connection
  • Malfunctioning mirror motors
  • Corroded terminals
  • Issues with the vehicle's body control module (BCM)
  • Communication network problems (e.g., J1850 bus issues)
  • Software glitches or programming errors

Common misdiagnoses

  • Faulty mirror control module
  • Wiring issues or shorts in the mirror circuit
  • Defective mirrors
  • Problems with the vehicle's body control module (BCM)
  • Communication issues with the CAN bus
  • Low battery voltage or power supply issues
  • Faulty connectors or terminals related to the mirror system

Troubleshooting steps

  1. 1. Check for Other Codes

    Use an OBD-II scanner to check for any additional trouble codes. Addressing other related codes may help resolve the U1794 code

  2. 2. Inspect Wiring and Connectors

    Visual Inspection: Check the wiring harness and connectors related to the mirrors for any signs of damage, corrosion, or loose connections

  3. 3. Repair or Replace

    Repair any damaged wires or connectors, and ensure all connections are secure

  4. 4. Test the Mirrors

    Functionality Check: Manually test the mirrors to ensure they are functioning correctly. If they are not responding, they may need to be replaced

  5. 5. Power Supply

    Verify that the mirrors are receiving the correct voltage and ground

  6. 6. Check the Body Control Module (BCM)

    The BCM often controls the mirrors. Inspect the BCM for any faults or issues

  7. 7. Reprogram or Replace

    If the BCM is faulty, it may need to be reprogrammed or replaced

  8. 8. Inspect the SCP Bus

    Bus Integrity: Check the integrity of the SCP bus. Look for shorts, opens, or other issues in the communication lines

  9. 9. Termination Resistors

    Ensure that the termination resistors are present and functioning correctly

  10. 10. Scan for Communication Issues

    Use a scan tool to monitor the communication on the SCP bus. Look for any irregularities or interruptions in communication

  11. 11. Signal Quality

    Check the signal quality on the bus lines to ensure they are within specifications

  12. 12. Check for Interference

    Look for any aftermarket devices or modifications that may be interfering with the SCP communication

  13. 13. Perform a Reset

    Clear the trouble codes using the OBD-II scanner and see if the code returns after a test drive. Sometimes, a reset can resolve temporary communication issues

  14. 14. Consult Technical Service Bulletins (TSBs)

    Check for any TSBs related to the U1794 code or mirror issues for your specific vehicle make and model. Manufacturers may have specific fixes or updates

  15. 15. 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 the problem more effectively. By following these troubleshooting steps, you should be able to identify and resolve the issue related to the U1794 code