AutoCodes – Chevrolet – P0851 Chevrolet

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

Quick Answer

The transmission manual shift shaft switch assembly, also known as the Internal Mode Switch (IMS), is a sliding contact switch attached to the manual shift shaft inside the transmission case. Common causes include Faulty Transmission Internal Mode Switch (IMS), Transmission Internal Mode Switch harness is open or shorted, Transmission Internal Mode Switch circuit poor electrical connection. 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 Chevrolet indicates Park/Neutral Position Switch Circuit Low Voltage.
Common causes: Common causes include Faulty Transmission Internal Mode Switch (IMS), Transmission Internal Mode Switch harness is open or shorted, Transmission Internal Mode Switch circuit poor electrical connection.
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.

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Code Popularity 4,817

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Intermediate (2 / 3)

What is this?

Table of contents Created and updated by William Orellana on Aug 03, 2022

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P0851 Chevrolet Description

The transmission manual shift shaft switch assembly, also known as the Internal Mode Switch (IMS), is a sliding contact switch attached to the manual shift shaft inside the transmission case. The Park/Neutral Position (PNP) Switch is integrated into the IMS and connects to the Transmission Control Module (TCM) lead frame through a short wire harness. The 5 inputs to the TCM from the transmission manual shift shaft switch assembly indicate the transmission gear selector lever position. This information is used for engine start enabling, engine controls as well as determining the transmission shift patterns.
The state of each input is available for display on the scan tool. The five input parameters represented are Signal A, Signal B, Signal C, Signal P (Parity), and Signal N (Park/Neutral Start Signal). Park/Neutral Signal is sent from the Park/Neutral switch directly to the Engine Control Module (ECM) and is used for engine start enable. The Park/Neutral Signal circuit is not connected to the TCM internally; the circuit uses the TCM as a pass-through connector only. The Diagnostic Trouble Code (DTC) will be set when the ECM detects the Park/Neutral switch signal equals 0 V, Low, when the IMS reports a Drive range.

OBDII Code P0851 Chevrolet - Park/Neutral Position Switch Circuit Low Voltage - AutoCodes.com — P0851 Chevrolet Code - Park/Neutral Position Switch Circuit Low Voltage

What does this mean?

What are the Possible Causes of the DTC P0851 Chevrolet?

Faulty Transmission Internal Mode Switch (IMS)
Transmission Internal Mode Switch harness is open or shorted
Transmission Internal Mode Switch circuit poor electrical connection
Faulty Control Solenoid Valve Assembly
Faulty Engine Control Module (ECM)

How to Fix the DTC P0851 Chevrolet?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0851 Chevrolet code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

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Information for Specific Chevrolet Models

P0851 2014 Chevrolet Silverado — Park/Neutral Position Switch Circuit Low Voltage
P0851 2015 Chevrolet Silverado — Park/Neutral Position Switch Circuit Low Voltage
P0851 2016 Chevrolet Silverado — Park/Neutral Position Switch Circuit Low Voltage
P0851 2017 Chevrolet Silverado — Park/Neutral Position Switch Circuit Low Voltage
P0851 2018 Chevrolet Silverado — Park/Neutral Position Switch Circuit Low Voltage

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 Chevrolet Code

1. What are the common symptoms of OBDII code P0851 in a Chevrolet related to the Park/Neutral Position Switch Circuit Low Voltage?

The common symptoms include difficulty starting the vehicle, issues shifting gears, and the inability to start the engine in Park or Neutral.

2. What are the possible causes of OBDII code P0851 in a Chevrolet?

Possible causes include a faulty park/neutral position switch, damaged wiring or connectors in the circuit, low voltage in the switch circuit, or a problem with the vehicle's computer system.

3. How can I diagnose the Park/Neutral Position Switch Circuit Low Voltage issue in a Chevrolet triggering code P0851?

Diagnosing the problem involves checking the park/neutral position switch for proper operation, inspecting the wiring and connectors for any damage, and testing the voltage in the switch circuit using a multimeter.

4. Can a DIY enthusiast repair the OBDII code P0851 related to the Park/Neutral Position Switch Circuit Low Voltage in a Chevrolet?

Yes, depending on the underlying cause, a DIY enthusiast with some mechanical experience can replace a faulty park/neutral position switch or repair damaged wiring or connectors to resolve the issue.

5. Is it safe to continue driving a Chevrolet with the OBDII code P0851 indicating a Park/Neutral Position Switch Circuit Low Voltage problem?

It is not recommended to drive the vehicle with this issue as it can lead to further damage or safety concerns, such as the vehicle stalling unexpectedly or difficulty shifting gears.

6. How much does it typically cost to repair OBDII code P0851 related to the Park/Neutral Position Switch Circuit Low Voltage in a Chevrolet?

The cost of repair can vary depending on the exact cause of the issue, but it may range from $100 to $300 for parts and labor if the park/neutral position switch needs to be replaced.

7. Can resetting the OBDII code P0851 related to the Park/Neutral Position Switch Circuit Low Voltage in a Chevrolet solve the problem temporarily?

Resetting the code may temporarily turn off the check engine light, but it will not fix the underlying issue causing the low voltage in the park/neutral position switch circuit.

8. How important is it to address the OBDII code P0851 in a Chevrolet indicating a Park/Neutral Position Switch Circuit Low Voltage problem?

It is crucial to address this issue promptly, as it can affect the drivability of the vehicle and potentially lead to more severe transmission or starting problems if left unresolved.

9. Are there any preventive measures to avoid triggering the OBDII code P0851 related to the Park/Neutral Position Switch Circuit Low Voltage in a Chevrolet?

Regular maintenance checks, such as inspecting the park/neutral position switch and its wiring during scheduled services, can help prevent issues that may trigger the P0851 trouble code.

10. Can extreme weather conditions or rough driving terrain contribute to the occurrence of OBDII code P0851 in a Chevrolet due to the Park/Neutral Position Switch Circuit Low Voltage?

Yes, extreme weather conditions or rough driving terrain can potentially damage the park/neutral position switch or its wiring, leading to low voltage issues and triggering the P0851 trouble code.