AutoCodes – GMC – P1839 2018 GMC Sierra

P1839 2018 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 2018 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 281

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 2018 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 2018 GMC Sierra - Internal Mode Switch 'C' Circuit Low Voltage - AutoCodes.com — P1839 2018 GMC Sierra Code - Internal Mode Switch 'C' Circuit Low Voltage

What does this mean?

What are the Possible Causes of the DTC P1839 2018 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 2018 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 2018 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 2018 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 2018 GMC Sierra Code

1. What are the common symptoms of OBDII code P1839 in a 2018 GMC Sierra?

- Common symptoms include issues with shifting gears, delayed gear engagement, and possible illumination of the Check Engine light.

2. What does the OBDII code P1839 'Internal Mode Switch 'C' Circuit Low Voltage' mean for a 2018 GMC Sierra?

- This code indicates that there is a low voltage condition detected in the internal mode switch 'C' circuit of the transmission range selector.

3. What are the potential causes of OBDII code P1839 in a 2018 GMC Sierra?

- Causes can include a faulty internal mode switch, damaged wiring or connectors in the circuit, low battery voltage, or a malfunctioning transmission control module (TCM).

4. How can I diagnose OBDII code P1839 in my 2018 GMC Sierra?

- Diagnosing this code typically involves using a scan tool to retrieve the trouble codes, checking the internal mode switch circuit for continuity and voltage, inspecting wiring and connectors for damage, and testing the TCM.

5. Can I continue to drive my 2018 GMC Sierra with OBDII code P1839?

- It is not recommended to continue driving with this code present, as it can lead to transmission issues and potential safety hazards. It's best to address the problem promptly.

6. How can I repair OBDII code P1839 in my 2018 GMC Sierra?

- Repair options may include replacing the internal mode switch, repairing or replacing damaged wiring and connectors, addressing low battery voltage issues, or replacing the TCM if necessary.

7. Is it possible to clear OBDII code P1839 in a 2018 GMC Sierra without fixing the underlying issue?

- While you can clear the code temporarily, it is likely to reappear until the root cause is addressed. It's important to fix the problem to prevent further transmission issues.

8. How much does it typically cost to repair OBDII code P1839 in a 2018 GMC Sierra?

- The cost of repair can vary depending on the specific cause of the code, parts needed, labor rates, and location. It's recommended to consult with a professional mechanic for an accurate estimate.

9. Are there any preventive measures to avoid OBDII code P1839 in a 2018 GMC Sierra?

- Regular maintenance, such as checking for wiring damage, ensuring proper battery voltage, and addressing any transmission issues promptly, can help prevent this code from occurring.

10. Can a DIY enthusiast with basic automotive knowledge fix OBDII code P1839 in a 2018 GMC Sierra?

- While some aspects of diagnosing and repairing this code may be within reach for DIY enthusiasts, it is recommended to consult with a professional mechanic for accurate diagnosis and repair to ensure the issue is properly resolved.