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P1839 2018 GMC Sierra Code - Internal Mode Switch 'C' Circuit Low Voltage

Quick Answer

The diagnostic trouble code P1839 for a 2018 GMC Sierra indicates an issue with the Internal Mode Switch 'C' Circuit Low Voltage. Common causes include Faulty Internal Mode Switch, Wiring or connection issues in the circuit, Corrosion or damage to the IMS connector. 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 Internal Mode Switch, Wiring or connection issues in the circuit, Corrosion or damage to the IMS connector.
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.
What is this?
Table of contents Created and updated by William Orellana on Sep 11, 2024
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Code P1839 2018 GMC Sierra Description

The diagnostic trouble code P1839 for a 2018 GMC Sierra indicates an issue with the Internal Mode Switch 'C' Circuit Low Voltage. This code is specifically related to the transmission control system of the vehicle. The Internal Mode Switch (IMS) is a component within the transmission that communicates the gear selection to the vehicle's onboard computer. The IMS provides information about the position of the gear selector lever, allowing the transmission to engage the correct gear.

OBDII Code P1839 2018 GMC Sierra - Internal Mode Switch 'C' Circuit Low Voltage
P1839 2018 GMC Sierra Code - Internal Mode Switch 'C' Circuit Low Voltage

Common Causes of P1839 2018 GMC Sierra

  1. Faulty Internal Mode Switch
  2. Wiring or connection issues in the circuit
  3. Corrosion or damage to the IMS connector
  4. Electrical system issues
  5. Faulty transmission control module

Symptoms of P1839 2018 GMC Sierra

  1. Erratic shifting behavior
  2. Difficulty shifting gears
  3. Transmission slipping
  4. Check engine light illuminated
  5. Reduced fuel efficiency

How to Fix P1839 2018 GMC Sierra

  1. Begin by diagnosing the specific cause of the low voltage signal from the Internal Mode Switch.
  2. Inspect the wiring and connections related to the IMS circuit for any damage or corrosion. Repair or replace as necessary.
  3. Test the Internal Mode Switch itself to determine if it is functioning properly. Replace the IMS if it is found to be faulty.
  4. Clear the diagnostic trouble code from the vehicle's onboard computer.
  5. Test drive the vehicle to ensure that the transmission is shifting correctly and that the code does not return.

Cost to Fix P1839 2018 GMC Sierra

The cost of repairing the Internal Mode Switch 'C' Circuit Low Voltage issue can vary depending on the specific cause of the problem. In general, the cost of replacing a faulty Internal Mode Switch can range from $150 to $300 for the part alone. Labor costs for diagnosing and repairing the issue can add an additional $100 to $200 or more, depending on the shop's hourly rates. Overall, the total repair cost for this issue may range from $250 to $500 or more, depending on the extent of the repairs needed. It is advisable to consult with a qualified mechanic or dealership to get an accurate estimate based on your specific vehicle and location.

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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.

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