WOMS
P code powertrain Medium severity

P0851 Park / Neutral Switch Input Circuit Low

The OBD2 code P0851 indicates a low voltage signal from the park/neutral switch input circuit, which may suggest a malfunction in the switch or its wiring, affecting the transmission's ability to determine if the...

Definition

The OBD2 code P0851 indicates a low voltage signal from the park/neutral switch input circuit, which may suggest a malfunction in the switch or its wiring, affecting the transmission's ability to determine if the vehicle is in park or neutral

Common causes

  • Faulty park/neutral switch
  • Damaged wiring or connectors
  • Poor electrical connections
  • Malfunctioning transmission control module (TCM)
  • Low transmission fluid level
  • Corroded terminals
  • Faulty engine control module (ECM)

Common misdiagnoses

  • Faulty transmission range sensor
  • Defective neutral safety switch
  • Wiring issues or shorts in the circuit
  • Malfunctioning transmission control module (TCM)
  • Incorrectly adjusted or misaligned shift linkage
  • Faulty engine control module (ECM)
  • Bad ground connections
  • Transmission fluid issues or low fluid levels

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 Park/Neutral Switch

    Locate the Park/Neutral switch (also known as the transmission range sensor) and visually inspect it for any signs of damage, corrosion, or loose connections

  3. 3. Ensure that the switch is properly aligned and securely mounted

  4. 4. Test the Switch

    Use a multimeter to test the continuity of the Park/Neutral switch. Check the resistance when the transmission is in the Park and Neutral positions

  5. 5. Compare the readings to the specifications in the vehicle's service manual

  6. 6. Check Wiring and Connectors

    Inspect the wiring harness and connectors leading to the Park/Neutral switch for any signs of wear, fraying, or damage

  7. 7. Look for any loose or corroded connections that could cause a poor electrical signal

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

    If the Park/Neutral switch and wiring are in good condition, the issue may lie with the Transmission Control Module (TCM)

  9. 9. Check for any software updates or known issues with the TCM for your specific vehicle model

  10. 10. Test the Battery and Charging System

    A weak battery or charging system can cause low voltage issues. Ensure the battery is fully charged and the charging system is functioning properly

  11. 11. Check Fuses

    Inspect the fuses related to the transmission and Park/Neutral switch circuits. Replace any blown fuses

  12. 12. Clear Codes and Test Drive

    After performing repairs or adjustments, 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 performing these steps, it may be necessary to consult a professional mechanic or technician who has experience with your specific vehicle make and model. By following these troubleshooting steps, you should be able to identify and resolve the issue related to the P0851 code. Always refer to the vehicle's service manual for specific procedures and specifications