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Engine-Codes – Generic – P0851

P0851 Code - Park/Neutral Position Switch Circuit Low Voltage

Quick Answer

The P0851 diagnostic trouble code (DTC) refers to a Park/Neutral Position (PNP) switch circuit with low voltage. Common causes include Faulty Park/Neutral Position switch, Wiring issues or damaged connectors in the PNP switch circuit, Corrosion or poor connections in the electrical system. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means
P0851 indicates Park/Neutral Position Switch Circuit Low Voltage.
Common causes
Common causes include Faulty Park/Neutral Position switch, Wiring issues or damaged connectors in the PNP switch circuit, Corrosion or poor connections in the electrical system.
Severity
High - diagnose this code as soon as possible.
Can I drive?
Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
What is this?
Table of contents Created and updated by William Orellana on Sep 11, 2024
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Code P0851 Description

The P0851 diagnostic trouble code (DTC) refers to a Park/Neutral Position (PNP) switch circuit with low voltage. The PNP switch, also known as the transmission range sensor, is a vital component in automatic transmissions that helps determine the gear position of the vehicle. The PNP switch sends signals to the engine control module (ECM) to inform it of whether the vehicle is in park or neutral. When the ECM detects low voltage from the PNP switch circuit, it triggers the P0851 code.

OBDII Code P0851 - Park/Neutral Position Switch Circuit Low Voltage
P0851 Code - Park/Neutral Position Switch Circuit Low Voltage

Common Causes of P0851

  1. Faulty Park/Neutral Position switch
  2. Wiring issues or damaged connectors in the PNP switch circuit
  3. Corrosion or poor connections in the electrical system
  4. ECM or transmission control module (TCM) malfunction
  5. Mechanical problems with the transmission range sensor

Symptoms of P0851

  1. Difficulty starting the engine
  2. Inability to shift gears or transmission stuck in one gear
  3. Vehicle not moving when put into drive or reverse
  4. Engine stalling when shifting into gear
  5. Check Engine Light illuminated on the dashboard

How to Fix P0851

  1. Begin by diagnosing the P0851 code using a diagnostic scan tool to verify the issue.
  2. Inspect the PNP switch and its wiring for any signs of damage, corrosion, or loose connections.
  3. Test the PNP switch using a multimeter to check for proper voltage and continuity.
  4. Replace the Park/Neutral Position switch if it is found to be faulty.
  5. Clear the DTC and test drive the vehicle to ensure the issue has been resolved.

Cost to Fix P0851

The typical repair costs for addressing a P0851 code can range from $150 to $400, including parts and labor. However, actual costs may vary depending on the specific vehicle make and model, as well as the location and labor rates of the auto repair shop. It is recommended to consult with a professional mechanic for an accurate estimate based on your individual circumstances.

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Code P0851 Information for Specific Makes

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

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