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P0879 Transmission Fluid Pressure Sensor/Switch "D" Circuit Intermittent

The OBD2 code P0879 indicates that there is an intermittent issue with the transmission fluid pressure sensor or switch "D" circuit, which may affect the transmission's ability to monitor fluid pressure accurately

Definition

The OBD2 code P0879 indicates that there is an intermittent issue with the transmission fluid pressure sensor or switch "D" circuit, which may affect the transmission's ability to monitor fluid pressure accurately

Common causes

  • Faulty transmission fluid pressure sensor/switch
  • Wiring issues (damaged, frayed, or corroded wires)
  • Poor electrical connections
  • Transmission control module (TCM) malfunction
  • Low transmission fluid level
  • Contaminated transmission fluid
  • Faulty transmission solenoid
  • Internal transmission problems

Common misdiagnoses

  • Faulty transmission control module (TCM)
  • Transmission fluid issues (low fluid, contamination)
  • Faulty transmission pressure sensor
  • Wiring or connector issues
  • Faulty transmission solenoids
  • Internal transmission problems
  • Engine control module (ECM) issues
  • Incorrectly diagnosed electrical problems

Troubleshooting steps

  1. 1. Check for Additional Codes

    Use an OBD-II scanner to check for any other related trouble codes. This can provide more context and help identify if there are other issues affecting the transmission

  2. 2. Inspect the Transmission Fluid

    Fluid Level: Ensure that the transmission fluid is at the correct level. Low fluid can cause pressure issues

  3. 3. Fluid Condition

    Check the condition of the fluid. It should be a bright red color and free of debris or a burnt smell. If the fluid is dark or smells burnt, it may need to be changed

  4. 4. Visual Inspection

    Wiring and Connectors: Inspect the wiring and connectors related to the Transmission Fluid Pressure Sensor. Look for signs of damage, corrosion, or loose connections

  5. 5. Sensor Condition

    Check the physical condition of the Transmission Fluid Pressure Sensor. If it appears damaged or worn, it may need to be replaced

  6. 6. Test the Transmission Fluid Pressure Sensor

    Use a multimeter to test the resistance of the sensor. Compare the readings to the specifications provided in the vehicle’s service manual

  7. 7. If possible, use a scan tool to monitor the sensor’s output while the vehicle is running. Look for any erratic readings

  8. 8. Check for Ground Issues

    Ensure that the sensor has a good ground connection. A poor ground can lead to intermittent signals

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

    Check for any issues with the TCM, as it processes the signals from the fluid pressure sensor. Ensure that the TCM is functioning correctly and that its connections are secure

  10. 10. Look for Mechanical Issues

    Inspect the transmission for any mechanical issues that could affect fluid pressure, such as a stuck valve or internal leaks

  11. 11. Perform a Transmission Fluid Change

    If the fluid is old or contaminated, consider performing a transmission fluid change. This can sometimes resolve issues related to pressure and sensor readings

  12. 12. Clear Codes and Test Drive

    After performing the above checks and repairs, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns

  13. 13. Consult a Professional

    If the issue persists after following these steps, it may be necessary to consult a professional mechanic or transmission specialist for further diagnosis.Conclusion Intermittent issues can be tricky to diagnose, so thoroughness is key. Following these steps should help you identify the root cause of the P0879 code and address it effectively