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P0851 2018 GMC Sierra Code - Park/Neutral Position Switch Circuit Low Voltage

Quick Answer

The P0851 diagnostic trouble code (DTC) on a 2018 GMC Sierra indicates a problem with the Park/Neutral Position (PNP) switch circuit having low voltage. Common causes include Faulty Park/Neutral Position (PNP) switch, Damaged wiring or connectors in the PNP switch circuit, Corrosion or debris affecting electrical connections. 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 2018 GMC Sierra indicates Park/Neutral Position Switch Circuit Low Voltage.
Common causes
Common causes include Faulty Park/Neutral Position (PNP) switch, Damaged wiring or connectors in the PNP switch circuit, Corrosion or debris affecting electrical connections.
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 08, 2024
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Code P0851 2018 GMC Sierra Description

The P0851 diagnostic trouble code (DTC) on a 2018 GMC Sierra indicates a problem with the Park/Neutral Position (PNP) switch circuit having low voltage. The PNP switch, also known as the Transmission Range Sensor (TRS), is an essential component of the vehicle's transmission system. Its primary function is to inform the engine control module (ECM) about the transmission's gear position, specifically when the vehicle is in Park or Neutral.

OBDII Code P0851 2018 GMC Sierra - Park/Neutral Position Switch Circuit Low Voltage
P0851 2018 GMC Sierra Code - Park/Neutral Position Switch Circuit Low Voltage

Common Causes of P0851 2018 GMC Sierra

  1. Faulty Park/Neutral Position (PNP) switch
  2. Damaged wiring or connectors in the PNP switch circuit
  3. Corrosion or debris affecting electrical connections
  4. ECM malfunction or software issues
  5. Physical damage to the PNP switch or related components

Symptoms of P0851 2018 GMC Sierra

  1. Difficulty starting the vehicle
  2. Inability to shift gears smoothly
  3. Dashboard warning lights illuminated
  4. Engine stalling or shutting off unexpectedly
  5. Transmission slipping or erratic behavior

How to Fix P0851 2018 GMC Sierra

  1. Begin by conducting a thorough inspection of the PNP switch, wiring, and connectors for any visible damage or corrosion.
  2. Use a multimeter to test the voltage output of the PNP switch and verify if it falls within the specified range. Replace the switch if necessary.
  3. Check and repair any damaged wiring or connectors in the PNP switch circuit.
  4. Clear the DTC from the ECM memory using a diagnostic scanner and perform a test drive to confirm that the issue has been resolved.
  5. If the problem persists, consult a professional mechanic for further diagnosis and potential ECM reprogramming or replacement.

Cost to Fix P0851 2018 GMC Sierra

The typical repair costs for addressing a P0851 code on a 2018 GMC Sierra can range from $100 to $300, depending on the exact cause of the issue and the necessary repairs. This estimate includes the cost of parts, such as a new PNP switch or wiring harness, as well as labor charges. It's important to note that diagnostic time and labor rates at auto repair shops can vary widely, so it's advisable to obtain quotes from multiple service providers to ensure a competitive price.

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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.

Frequently Asked Questions about P0851 2018 GMC Sierra Code

1. What are the common symptoms of OBDII code P0851 in a 2018 GMC Sierra?

- Common symptoms include difficulty starting the vehicle, the engine stalling, and the inability to shift out of park.

2. What does the OBDII code P0851 "Park/Neutral Position Switch Circuit Low Voltage" mean for a 2018 GMC Sierra?

- This code indicates that the voltage in the park/neutral position switch circuit is lower than the specified range.

3. What are the possible causes of OBDII code P0851 in a 2018 GMC Sierra?

- Potential causes include a faulty park/neutral position switch, damaged wiring or connectors in the circuit, or a malfunctioning transmission range sensor.

4. How can I diagnose the OBDII code P0851 in my 2018 GMC Sierra?

- You can diagnose this code by checking the park/neutral position switch for proper operation, inspecting the wiring and connectors for damage, and testing the transmission range sensor.

5. Can I continue to drive my 2018 GMC Sierra with the OBDII code P0851 present?

- It is not recommended to drive the vehicle with this code present, as it can lead to further transmission problems or safety issues.

6. How can I repair OBDII code P0851 in my 2018 GMC Sierra?

- Repair options include replacing the park/neutral position switch, repairing any damaged wiring or connectors, or replacing the transmission range sensor.

7. Will resetting the OBDII code P0851 in my 2018 GMC Sierra make it go away permanently?

- Resetting the code may temporarily clear the error, but if the underlying issue is not addressed, the code is likely to reappear.

8. Can a DIY enthusiast fix the OBDII code P0851 in a 2018 GMC Sierra?

- Depending on the level of expertise, a DIY enthusiast may be able to diagnose and repair this code, but it is recommended to consult a professional for accurate diagnosis and repair.

9. How much does it cost to repair OBDII code P0851 in a 2018 GMC Sierra?

- The cost of repairs can vary depending on the cause of the issue and the labor rates in your area. It is best to obtain quotes from local mechanics or dealerships.

10. Is OBDII code P0851 a common issue in 2018 GMC Sierra vehicles?

- While not extremely common, the P0851 code can be encountered in 2018 GMC Sierra vehicles due to issues with the park/neutral position switch circuit.

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