AutoCodes – GMC – P1839 2017 GMC Sierra

P1839 2017 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 2017 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 303

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 2017 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 2017 GMC Sierra - Internal Mode Switch 'C' Circuit Low Voltage - AutoCodes.com — P1839 2017 GMC Sierra Code - Internal Mode Switch 'C' Circuit Low Voltage

What does this mean?

What are the Possible Causes of the DTC P1839 2017 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 2017 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 2017 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 2017 GMC Sierra code?

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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 2017 GMC Sierra Code

1. What are the common symptoms of OBDII code P1839 in a 2017 GMC Sierra?

The common symptoms of OBDII code P1839 (Internal Mode Switch 'C' Circuit Low Voltage) in a 2017 GMC Sierra may include issues with shifting gears, erratic transmission behavior, and a malfunction indicator light (MIL) on the dashboard.

2. What are the possible causes of OBDII code P1839 in a 2017 GMC Sierra?

Possible causes of OBDII code P1839 in a 2017 GMC Sierra include a faulty internal mode switch, damaged wiring or connectors in the circuit, low voltage in the switch circuit, or a malfunctioning transmission control module (TCM).

3. How can I diagnose OBDII code P1839 in my 2017 GMC Sierra?

To diagnose OBDII code P1839 in a 2017 GMC Sierra, you can use a diagnostic scanner to read the code and perform a thorough inspection of the internal mode switch, wiring, and connectors. Testing the voltage in the circuit and checking for any visible signs of damage can help pinpoint the issue.

4. Can I continue driving my 2017 GMC Sierra with OBDII code P1839?

It is not recommended to continue driving your 2017 GMC Sierra with OBDII code P1839, as it can lead to further transmission problems and potential safety hazards. It is advisable to address the issue promptly to avoid more significant damage.

5. How do I repair OBDII code P1839 in my 2017 GMC Sierra?

Repairing OBDII code P1839 in a 2017 GMC Sierra may involve replacing the internal mode switch, repairing or replacing damaged wiring or connectors, checking and correcting the voltage in the circuit, or reprogramming the transmission control module (TCM) if necessary.

6. Can a DIY enthusiast fix OBDII code P1839 in a 2017 GMC Sierra?

While some DIY enthusiasts may be able to diagnose and repair OBDII code P1839 in a 2017 GMC Sierra, it is recommended to seek professional help, especially when dealing with transmission-related issues. Proper diagnosis and repair are crucial to ensure the problem is addressed correctly.

7. Is OBDII code P1839 a serious issue in a 2017 GMC Sierra?

OBDII code P1839 (Internal Mode Switch 'C' Circuit Low Voltage) in a 2017 GMC Sierra should be taken seriously, as it can affect the transmission's performance and reliability. Ignoring this code can lead to transmission problems and potentially costly repairs if not addressed promptly.

8. How much does it cost to fix OBDII code P1839 in a 2017 GMC Sierra?

The cost to fix OBDII code P1839 in a 2017 GMC Sierra can vary depending on the root cause of the issue, the extent of the repairs needed, and labor costs. It is advisable to get a diagnostic assessment from a qualified mechanic to determine the exact cost.

9. Can OBDII code P1839 in a 2017 GMC Sierra cause other problems if left untreated?

If left untreated, OBDII code P1839 in a 2017 GMC Sierra can potentially cause further damage to the transmission system, leading to more severe issues such as transmission slippage, harsh shifting, or total transmission failure. It is essential to address this code promptly to prevent additional problems.

10. How long does it take to repair OBDII code P1839 in a 2017 GMC Sierra?

The time it takes to repair OBDII code P1839 in a 2017 GMC Sierra can vary depending on the exact cause of the issue, the availability of parts, and the mechanic's expertise. In general, repairs for this code can take a few hours to a full day to complete.