AutoCodes – GMC – P0850 GMC

P0850 GMC Code - Park/Neutral Position Switch Circuit

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: P0850 GMC indicates Park/Neutral Position Switch Circuit.
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 2,105

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 P0850 GMC 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 P0850 GMC - Park/Neutral Position Switch Circuit - AutoCodes.com — P0850 GMC Code - Park/Neutral Position Switch Circuit

What does this mean?

What are the Possible Causes of the DTC P0850 GMC?

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 P0850 GMC?

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 P0850 GMC 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.

Need more information about the P0850 GMC code?

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Need Help with the Code?

Get the P0850 GMC code diagnosed by a professional: Find a repair shop in your area

Information for Specific GMC Models

P0850 2014 GMC Sierra — Park/Neutral Position Switch Circuit
P0850 2015 GMC Sierra — Park/Neutral Position Switch Circuit
P0850 2016 GMC Sierra — Park/Neutral Position Switch Circuit
P0850 2017 GMC Sierra — Park/Neutral Position Switch Circuit
P0850 2018 GMC Sierra — Park/Neutral Position Switch Circuit

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 P0850 GMC Code

1. What does the OBDII code P0850 mean on a GMC vehicle?

P0850 indicates a problem with the Park/Neutral Position (PNP) Switch Circuit, which monitors the transmission's gear position to ensure the vehicle starts only in Park or Neutral.

2. What are the common symptoms of the P0850 code on a GMC?

Symptoms may include the vehicle not starting in Park or Neutral, the Check Engine Light turning on, or erratic shifting behavior.

3. What causes the P0850 code to appear on a GMC?

Common causes include a faulty Park/Neutral Position switch, damaged or corroded wiring, poor electrical connections, or a malfunctioning Transmission Control Module (TCM).

4. Can I drive my GMC with a P0850 code?

Driving with a P0850 code is not recommended, as it can lead to starting issues or unsafe shifting behavior, potentially causing drivability problems.

5. How is the P0850 code diagnosed?

A technician will use a scan tool to check for the code, inspect the Park/Neutral Position switch, test the wiring for continuity, and verify proper operation of the transmission system.

6. How do I fix the P0850 code on a GMC?

Repairs may involve replacing the Park/Neutral Position switch, repairing damaged wiring, cleaning corroded connections, or reprogramming the TCM if necessary.

7. How much does it cost to fix the P0850 code on a GMC?

Repair costs vary but typically range from $150 to $400, depending on whether the issue is with the switch, wiring, or additional components.

8. Can a bad battery cause the P0850 code on a GMC?

While unlikely, a weak or failing battery can sometimes contribute to electrical issues, which may indirectly affect the Park/Neutral Position Circuit.

9. Is it possible to reset the P0850 code without repairs?

Clearing the code with a scan tool may temporarily remove it, but if the underlying issue isnâ€™t resolved, the code will likely return.

10. What happens if the P0850 code is ignored?

Ignoring the P0850 code can lead to starting difficulties, transmission malfunctions, and potential safety risks, so addressing it promptly is important.