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P0991 Transmission Fluid Pressure Sensor/Switch "E" Circuit Intermittent

The OBD2 code P0991 indicates that there is an intermittent issue with the transmission fluid pressure sensor or switch "E" circuit, which may affect the transmission's performance and operation

Definition

The OBD2 code P0991 indicates that there is an intermittent issue with the transmission fluid pressure sensor or switch "E" circuit, which may affect the transmission's performance and operation

Common causes

  • Faulty transmission fluid pressure sensor
  • Damaged wiring or connectors
  • Poor electrical connections
  • Low transmission fluid level
  • Contaminated transmission fluid
  • Faulty transmission control module (TCM)
  • Internal transmission issues

Common misdiagnoses

  • Faulty transmission fluid pressure sensor
  • Wiring issues or short circuits in the sensor circuit
  • Transmission control module (TCM) failure
  • Low transmission fluid level or contamination
  • Faulty transmission solenoids
  • Internal transmission problems
  • Engine control module (ECM) issues
  • Incorrectly installed or damaged transmission components

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 Wiring and Connectors

    Visual Inspection: Check the wiring harness and connectors associated with the Transmission Fluid Pressure Sensor. Look for signs of damage, corrosion, fraying, or loose connections

  3. 3. Connector Condition

    Ensure that the connectors are securely attached and free of dirt or moisture

  4. 4. Test the Transmission Fluid Pressure Sensor

    Resistance Check: Use a multimeter to measure the resistance of the sensor. Compare the readings to the specifications provided in the vehicle’s service manual

  5. 5. Voltage Check

    With the ignition on (engine off), check the voltage at the sensor connector. Ensure it matches the expected voltage as per the manufacturer’s specifications

  6. 6. Check Transmission Fluid Level and Condition

    Fluid Level: Ensure that the transmission fluid is at the correct level. Low fluid can cause erratic sensor readings

  7. 7. Fluid Condition

    Inspect the fluid for contamination, burning smell, or unusual color. If the fluid is dirty or burnt, consider a fluid change

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

    Check for any signs of damage or corrosion on the TCM. Ensure that it is functioning properly and that there are no software issues

  9. 9. Perform a Wiggle Test

    With the vehicle running, gently wiggle the wiring harness and connectors related to the transmission fluid pressure sensor. If the code returns or the transmission behavior changes, it may indicate a wiring issue

  10. 10. Check for Ground Issues

    Ensure that the ground connections for the transmission fluid pressure sensor and TCM are secure and free of corrosion

  11. 11. Test the Circuit

    Use a multimeter to perform a continuity test on the circuit between the sensor and the TCM. Look for any breaks or shorts in the wiring

  12. 12. Replace the Sensor (if necessary)

    If the sensor is found to be faulty based on your tests, replace it with a new one. Ensure that you clear the codes and test drive the vehicle to see if the issue is resolved

  13. 13. Clear Codes and Test Drive

    After making repairs, clear the trouble codes using the OBD-II scanner and take the vehicle for a test drive to see if the code returns.1

  14. 14. Consult a Professional

    If the issue persists after following these steps, it may be best to consult a professional mechanic or technician who has experience with transmission issues. By following these troubleshooting steps, you should be able to identify the cause of the P0991 code and take appropriate action to resolve it