AutoCodes – GMC – P1839 2016 GMC Sierra

P1839 2016 GMC Sierra Code - Internal Mode Switch 'C' Circuit Low Voltage

Quick Answer

The internal mode switch indicates the Transmission Control Module (TCM) which gear position the vehicle operator has selected. Common causes include Faulty Transmission Internal Mode Switch, 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: P1839 2016 GMC Sierra indicates Internal Mode Switch 'C' Circuit Low Voltage.
Common causes: Common causes include Faulty Transmission Internal Mode Switch, 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 245

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Mar 23, 2024

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P1839 2016 GMC Sierra Description

The internal mode switch indicates the Transmission Control Module (TCM) which gear position the vehicle operator has selected. The internal mode switch consists of 5 separate hall effect switches. Each hall effect switch is supplied with a 9 V reference circuit and a signal circuit from the TCM. Each signal circuit for each gear selector position will have either a voltage reading of 0.70–0.96 V indicating On or 1.68–2.38 V indicating Off. The voltage values on each internal mode switch circuit will change and are dependent on the position of the gear selector. The state of each internal mode switch A/B/C/P/S signal circuit is displayed on the scan tool. The Diagnostic Trouble Code (DTC) will be set when the TCM has detected the internal mode switch C signal circuit voltage is less than 0.7 V, for 1.75 s.

OBDII Code P1839 2016 GMC Sierra - Internal Mode Switch 'C' Circuit Low Voltage - AutoCodes.com — P1839 2016 GMC Sierra Code - Internal Mode Switch 'C' Circuit Low Voltage

What does this mean?

What are the Possible Causes of the DTC P1839 2016 GMC Sierra?

Faulty Transmission Internal Mode Switch
Transmission Internal Mode Switch harness is open or shorted
Transmission Internal Mode Switch circuit poor electrical connection
Faulty Transmission Control Module (TCM)

How to Fix the DTC P1839 2016 GMC Sierra?

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 P1839 2016 GMC Sierra 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 P1839 2016 GMC Sierra code?

Need more information on how to fix the P1839 2016 GMC Sierra code? Get Access to Factory Service Manuals

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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 P1839 2016 GMC Sierra Code

What does the OBDII code P1839 mean on a 2016 GMC Sierra?

P1839 indicates a low voltage issue in the Internal Mode Switch 'C' circuit, which is part of the transmission's range sensor system.

What are the common symptoms of code P1839 in a 2016 GMC Sierra?

Common symptoms include erratic transmission shifting, the inability to shift into certain gears, the transmission stuck in one gear, or the illumination of the check engine light.

What causes the P1839 code to appear?

The most common causes are faulty wiring or connectors in the Internal Mode Switch 'C' circuit, a failed internal mode switch (range sensor), or a problem with the transmission control module (TCM).

Can a bad battery cause the P1839 code?

Yes, a weak or failing battery can sometimes lead to low voltage issues that might trigger this code.

How do you diagnose the P1839 code on a 2016 GMC Sierra?

Diagnosis involves checking the wiring and connectors in the circuit for damage, testing the internal mode switch for proper operation, and verifying voltage and continuity in the circuit using a multimeter.

Can I drive my 2016 GMC Sierra with the P1839 code?

Driving with this code is not recommended, as it can lead to erratic shifting or further damage to the transmission system.

How much does it cost to repair the P1839 code on a 2016 GMC Sierra?

Repairs can range from $100 to $500, depending on whether the issue is a simple wiring fix or requires replacing the internal mode switch.

Will clearing the code fix the problem?

Clearing the code will only temporarily turn off the check engine light. The underlying issue causing the low voltage must be addressed to prevent the code from returning.

What tools are needed to troubleshoot the P1839 code?

Youâ€™ll need an OBDII scanner, a multimeter to test voltage and continuity, and possibly wiring diagrams for the transmission system.

Is the P1839 code related to other transmission codes?

Yes, it can be related to other transmission range sensor or internal mode switch codes, as they all involve the same system. Additional codes may provide further insight into the issue.