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P0979 Shift Solenoid C Control Circuit Low

The OBD2 code P0979 indicates a problem with the shift solenoid C control circuit, specifically that the circuit is reading a low voltage or signal, which may affect the transmission's shifting performance

Definition

The OBD2 code P0979 indicates a problem with the shift solenoid C control circuit, specifically that the circuit is reading a low voltage or signal, which may affect the transmission's shifting performance

Common causes

  • Faulty shift solenoid C
  • Wiring issues (shorts or open circuits)
  • Poor electrical connections
  • Faulty transmission control module (TCM)
  • Low transmission fluid levels
  • Contaminated transmission fluid
  • Internal transmission failure

Common misdiagnoses

  • Faulty transmission control module (TCM)
  • Wiring issues or shorts in the harness
  • Faulty shift solenoid C
  • Low transmission fluid level or contamination
  • Faulty transmission fluid temperature sensor
  • Internal transmission failure
  • Incorrectly diagnosed engine control module (ECM) issues
  • Problems with other shift solenoids
  • Faulty connectors or terminals
  • Misinterpretation of symptoms related to other transmission codes

Troubleshooting steps

  1. 1. 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 if there are related issues

  2. 2. Inspect Wiring and Connectors

  3. 3. Visually inspect the wiring and connectors associated with the shift solenoid. Look for signs of damage, corrosion, or loose connections

  4. 4. Pay special attention to the wiring harness that connects to the transmission and the solenoid itself

  5. 5. Test the Shift Solenoid

  6. 6. If accessible, test the shift solenoid C for proper operation. This can often be done by measuring the resistance across the solenoid terminals with a multimeter. Refer to the vehicle's service manual for the specific resistance values

  7. 7. If the solenoid is faulty, it may need to be replaced

  8. 8. Check the Transmission Fluid

  9. 9. Ensure that the transmission fluid is at the correct level and in good condition. Low or dirty fluid can affect solenoid operation

  10. 10. If the fluid is dirty, consider performing a transmission fluid change

  11. 11. Inspect the Transmission Control Module (TCM)

  12. 12. Check for any issues with the TCM, which controls the operation of the shift solenoids. Ensure that it is receiving proper power and ground signals

  13. 13. If necessary, test the TCM for faults or consider reprogramming it if updates are available

  14. 14. Test Voltage and Ground

  15. 15. Use a multimeter to check for proper voltage and ground at the solenoid connector. Ensure that the solenoid is receiving the correct voltage when commanded by the TCM

  16. 16. If there is no voltage or ground, trace the circuit back to find the source of the issue

  17. 17. Check for Short Circuits

  18. 18. Inspect the circuit for any short circuits that may be causing the low voltage reading. This can include checking for damaged insulation or pinched wires

  19. 19. Clear Codes and Test Drive

  20. 20. After performing any repairs or replacements, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns

  21. 21. Consult a Professional

  22. 22. If the issue persists after performing these steps, it may be necessary to consult a professional mechanic or technician who has experience with transmission issues and can perform more advanced diagnostics. By following these steps, you should be able to identify and address the cause of the P0979 code. Always refer to the specific service manual for your vehicle for detailed procedures and specifications