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P0891 TCM Power Relay Sense Circuit High

The OBD2 code P0891 indicates a problem with the Transmission Control Module (TCM) power relay sense circuit, specifically that the circuit is reading a high voltage when it should not be

Definition

The OBD2 code P0891 indicates a problem with the Transmission Control Module (TCM) power relay sense circuit, specifically that the circuit is reading a high voltage when it should not be

Common causes

  • Faulty TCM power relay
  • Wiring issues (shorts or open circuits)
  • Poor connections or corroded terminals
  • Faulty Transmission Control Module (TCM)
  • Malfunctioning power supply to the TCM
  • Blown fuses
  • Grounding issues in the circuit

Common misdiagnoses

  • Transmission Control Module (TCM) failure
  • Faulty power relay
  • Wiring issues or shorts
  • Battery or charging system problems
  • Engine Control Module (ECM) issues
  • Transmission fluid issues
  • Grounding problems
  • Faulty sensors related to transmission
  • Corroded connectors
  • Software or programming errors

Troubleshooting steps

  1. 1. Check for Additional Codes

    Before proceeding, check for any other related trouble codes that may provide more context to the issue

  2. 2. Inspect the TCM Power Relay

  3. 3. Locate the TCM power relay in the fuse box or relay panel

  4. 4. Inspect the relay for any signs of damage or corrosion

  5. 5. Swap the relay with a similar one (if available) to see if the problem persists

  6. 6. Examine Wiring and Connectors

  7. 7. Inspect the wiring and connectors associated with the TCM and the power relay for any signs of damage, fraying, or corrosion

  8. 8. Ensure that all connections are secure and free of dirt or moisture

  9. 9. Test the TCM Power Relay

  10. 10. Use a multimeter to test the relay. Check for continuity and proper operation when energized

  11. 11. If the relay is faulty, replace it

  12. 12. Check Power and Ground

  13. 13. Verify that the TCM is receiving the correct voltage and ground. Use a multimeter to check the voltage at the TCM connector

  14. 14. Ensure that the ground connection is solid and free of corrosion

  15. 15. Inspect the TCM

  16. 16. If the relay and wiring are in good condition, the issue may lie within the TCM itself. Check for any signs of damage or overheating

  17. 17. If possible, test the TCM in another vehicle or replace it with a known good unit to see if the problem resolves

  18. 18. Check for Short Circuits

  19. 19. Inspect the wiring harness for any short circuits that may be causing the high voltage reading. Look for pinched wires or areas where the insulation may be damaged

  20. 20. Clear Codes and Test Drive

  21. 21. After performing the above checks and repairs, clear the trouble codes using an OBD-II scanner

  22. 22. Take the vehicle for a test drive to see if the code returns

  23. 23. Consult a Professional

  24. 24. If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or technician who has access to advanced diagnostic tools and equipment. By following these troubleshooting steps, you should be able to identify and resolve the issue related to the P0891 code