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P1909 Trans Temp Sensor Circuit Open or Shorted to Pwr or Gnd

The OBD2 code P1909 indicates a malfunction in the transmission temperature sensor circuit, specifically that the circuit is either open (disconnected) or shorted to power or ground, which can affect the sensor's...

Definition

The OBD2 code P1909 indicates a malfunction in the transmission temperature sensor circuit, specifically that the circuit is either open (disconnected) or shorted to power or ground, which can affect the sensor's ability to provide accurate temperature readings

Common causes

  • Faulty transmission temperature sensor
  • Damaged wiring or connectors
  • Short circuit in the wiring harness
  • Open circuit in the wiring harness
  • Corroded or loose electrical connections
  • Faulty engine control module (ECM)
  • Poor ground connection
  • Water intrusion or moisture in connectors

Common misdiagnoses

  • Transmission control module (TCM) failure
  • Faulty transmission fluid temperature sensor
  • Wiring issues or damaged connectors
  • Incorrect transmission fluid level
  • Faulty engine control module (ECM)
  • Other sensor failures (e.g., coolant temperature sensor)
  • Software or calibration issues
  • Transmission overheating problems
  • Grounding issues in the electrical system
  • Faulty or damaged transmission solenoids

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 additional context for the issue

  2. 2. Inspect the Wiring and Connectors

    Visual Inspection: Look for any visible damage to the wiring harness, connectors, or the transmission temperature sensor itself. Check for frayed wires, corrosion, or loose connections

  3. 3. Connector Condition

    Ensure that the connectors are clean and securely attached. Corrosion or dirt can cause poor connections

  4. 4. Test the Transmission Temperature Sensor

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

  5. 5. Sensor Functionality

    If the resistance is out of range, the sensor may be faulty and require replacement

  6. 6. Check for Shorts or Opens in the Circuit

    Continuity Test: With the vehicle off, perform a continuity test on the wiring between the sensor and the engine control module (ECM). Look for any breaks in the wire

  7. 7. Short to Ground or Power

    Check for shorts to ground or power by measuring voltage at the sensor connector with the ignition on. If you find voltage where there shouldn’t be any, there may be a short

  8. 8. Inspect the ECM

    Connector Check: Ensure that the ECM connectors are secure and free of corrosion

  9. 9. Signal Check

    If possible, check the signal coming from the transmission temperature sensor to the ECM. This may require a scan tool capable of live data monitoring

  10. 10. Check for Ground Issues

    Ensure that the ground connections for the transmission temperature sensor and the ECM are secure and free of corrosion. A poor ground can lead to erroneous readings

  11. 11. Clear Codes and Test Drive

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

  12. 12. Professional Help

    If you are unable to resolve the issue after these steps, it may be best to consult a professional mechanic or technician who has experience with transmission systems and OBD-II diagnostics. By following these steps, you should be able to identify the cause of the P1909 code and take appropriate action to resolve it