Engine-CodesGMC – P1839 2015 GMC Sierra

P1839 2015 GMC Sierra Code - Internal Mode Switch 'C' Circuit Low Voltage

Quick Answer

The P1839 diagnostic trouble code (DTC) for the 2015 GMC Sierra indicates an issue with the Internal Mode Switch 'C' Circuit Low Voltage. Common causes include Faulty internal mode switch, Damaged wiring or connectors in the circuit, Malfunctioning TCM. 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 2015 GMC Sierra indicates Internal Mode Switch 'C' Circuit Low Voltage.
Common causes
Common causes include Faulty internal mode switch, Damaged wiring or connectors in the circuit, Malfunctioning TCM.
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.
Table of contents Created and updated by William Orellana on Sep 11, 2024
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Code P1839 2015 GMC Sierra Description

The P1839 diagnostic trouble code (DTC) for the 2015 GMC Sierra indicates an issue with the Internal Mode Switch 'C' Circuit Low Voltage. The internal mode switch (IMS) is a component of the transmission control system that helps the vehicle's computer determine the position of the transmission gear selector. In this case, a low voltage reading in the circuit associated with switch 'C' has been detected, signaling a potential problem.

OBDII Code P1839 2015 GMC Sierra - Internal Mode Switch 'C' Circuit Low Voltage
P1839 2015 GMC Sierra Code - Internal Mode Switch 'C' Circuit Low Voltage

Common Causes of P1839 2015 GMC Sierra

  1. Faulty internal mode switch
  2. Damaged wiring or connectors in the circuit
  3. Malfunctioning TCM
  4. Issues with the vehicle's battery or electrical system
  5. Corrosion or moisture in the circuit

Symptoms of P1839 2015 GMC Sierra

  1. Incorrect gear shifting
  2. Hesitation or jerking when accelerating
  3. Poor fuel efficiency
  4. Transmission slipping
  5. Illumination of the check engine light

How to Fix P1839 2015 GMC Sierra

  1. Perform a thorough inspection of the internal mode switch 'C' circuit, including wiring and connectors.
  2. Test the internal mode switch for proper operation and voltage readings.
  3. Check the TCM for any fault codes and perform a reset if necessary.
  4. Repair or replace any damaged wiring or connectors in the circuit.
  5. Clear the DTC and test drive the vehicle to ensure the issue has been resolved.

Cost to Fix P1839 2015 GMC Sierra

The typical repair costs for addressing the Internal Mode Switch 'C' Circuit Low Voltage issue can vary depending on the specific cause of the problem and the extent of repairs needed. In general, parts such as a new internal mode switch or wiring harness may cost between $100 to $300, while labor costs can range from $150 to $300. Overall, the total repair costs for this issue may amount to approximately $250 to $600.

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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 2015 GMC Sierra Code

1. What are the common symptoms of OBDII code P1839 on a 2015 GMC Sierra?

- Common symptoms include issues with shifting gears, rough or erratic shifting, and the check engine light being illuminated.

2. What does the OBDII code P1839 'Internal Mode Switch 'C' Circuit Low Voltage' mean for a 2015 GMC Sierra?

- This code indicates a problem with the internal mode switch 'C' circuit, specifically low voltage being detected.

3. What are the possible causes of OBDII code P1839 on a 2015 GMC Sierra?

- Possible causes include a faulty internal mode switch, damaged wiring or connectors in the circuit, or a problem with the transmission control module.

4. How can I diagnose the Internal Mode Switch 'C' Circuit Low Voltage issue on my 2015 GMC Sierra?

- Diagnosing this issue typically involves checking the internal mode switch for proper operation, inspecting the wiring and connectors for damage, and testing the voltage in the circuit.

5. Can OBDII code P1839 on a 2015 GMC Sierra cause any serious damage if left unaddressed?

- Ignoring this code can lead to transmission shifting issues and potential further damage to the transmission system if not repaired promptly.

6. Is it safe to continue driving my 2015 GMC Sierra with the Internal Mode Switch 'C' Circuit Low Voltage issue?

- It is not recommended to continue driving the vehicle with this issue as it can affect the transmission's performance and potentially lead to further damage.

7. How can I repair OBDII code P1839 on my 2015 GMC Sierra?

- Repairing this code may involve replacing the internal mode switch, repairing or replacing damaged wiring or connectors, or addressing any issues with the transmission control module.

8. Can I reset the check engine light after addressing the Internal Mode Switch 'C' Circuit Low Voltage problem on my 2015 GMC Sierra?

- Yes, once the issue has been repaired and the fault codes cleared, the check engine light can be reset using an OBDII scanner or by disconnecting the vehicle's battery for a few minutes.

9. Is it necessary to have a professional mechanic address the OBDII code P1839 on a 2015 GMC Sierra?

- While some DIY enthusiasts may be able to diagnose and repair this issue, it is recommended to have a professional mechanic with experience in transmission systems handle the repair to ensure it is done correctly.

10. How long does it typically take to fix the Internal Mode Switch 'C' Circuit Low Voltage issue on a 2015 GMC Sierra?

- The repair time can vary depending on the exact cause of the issue, but it may take a few hours to a full day to diagnose and fix the problem.

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