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P1838 2015 GMC Sierra Code - Internal Mode Switch 'A' Circuit High Voltage

Quick Answer

The P1838 diagnostic trouble code (DTC) for a 2015 GMC Sierra indicates an issue with the Internal Mode Switch 'A' Circuit High Voltage. Common causes include Faulty Internal Mode Switch (IMS) sensor, Damaged wiring or connectors in the IMS 'A' circuit, Malfunctioning transmission control module. 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
P1838 2015 GMC Sierra indicates Internal Mode Switch 'A' Circuit High Voltage.
Common causes
Common causes include Faulty Internal Mode Switch (IMS) sensor, Damaged wiring or connectors in the IMS 'A' circuit, Malfunctioning transmission control module.
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 12, 2024
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Code P1838 2015 GMC Sierra Description

The P1838 diagnostic trouble code (DTC) for a 2015 GMC Sierra indicates an issue with the Internal Mode Switch 'A' Circuit High Voltage. The Internal Mode Switch (IMS) is a component within the transmission that communicates the gear selection to the vehicle's control module. When the IMS 'A' circuit registers a high voltage, it means that there is an electrical problem within the circuit that is causing it to operate outside of the normal parameters. This can lead to incorrect gear selection, transmission shifting issues, and potentially unsafe driving conditions.

OBDII Code P1838 2015 GMC Sierra - Internal Mode Switch 'A' Circuit High Voltage
P1838 2015 GMC Sierra Code - Internal Mode Switch 'A' Circuit High Voltage

Common Causes of P1838 2015 GMC Sierra

  1. Faulty Internal Mode Switch (IMS) sensor
  2. Damaged wiring or connectors in the IMS 'A' circuit
  3. Malfunctioning transmission control module
  4. Corrosion or moisture in the electrical connections
  5. Electrical short or open circuit in the IMS 'A' circuit

Symptoms of P1838 2015 GMC Sierra

  1. Erratic shifting or difficulty shifting gears
  2. Harsh gear changes or slipping transmission
  3. Check Engine Light illuminated on the dashboard
  4. Reduced fuel efficiency or engine performance
  5. Transmission stuck in one gear

How to Fix P1838 2015 GMC Sierra

  1. Begin by conducting a thorough diagnostic scan to confirm the P1838 code and identify the specific cause of the high voltage in the IMS 'A' circuit.
  2. Inspect the wiring and connectors in the circuit for any signs of damage, corrosion, or loose connections. Repair or replace any faulty components as needed.
  3. Test the Internal Mode Switch (IMS) sensor to ensure it is functioning correctly. Replace the sensor if it is found to be faulty.
  4. Clear the DTC from the vehicle's memory using a scan tool and test drive the vehicle to verify that the issue has been resolved.
  5. If the problem persists, further diagnostics may be required to pinpoint the exact cause of the high voltage in the IMS 'A' circuit, such as testing the transmission control module or conducting a voltage drop test on the circuit.

Cost to Fix P1838 2015 GMC Sierra

The typical repair costs for addressing the P1838 code on a 2015 GMC Sierra can vary depending on the specific cause of the issue. In general, the cost of replacing a faulty Internal Mode Switch (IMS) sensor can range from $150 to $300, while repairing damaged wiring or connectors may cost between $100 and $200. If the transmission control module needs to be replaced, the cost can be significantly higher, ranging from $500 to $1000 or more.

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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 P1838 2015 GMC Sierra Code

1. What does the OBDII code P1838 mean on a 2015 GMC Sierra?

P1838 indicates that the Internal Mode Switch (IMS) 'A' circuit is experiencing a high voltage condition, which can affect transmission operation.

2. What are the common symptoms of code P1838 on a 2015 GMC Sierra?

Symptoms may include the transmission stuck in one gear, erratic shifting, the Check Engine Light illuminating, or reduced vehicle performance.

3. What causes the P1838 code in a 2015 GMC Sierra?

Common causes include a faulty Internal Mode Switch, damaged wiring or connectors in the IMS circuit, or issues with the Transmission Control Module (TCM).

4. Can a loose or corroded connection cause the P1838 code?

Yes, loose or corroded electrical connections in the IMS circuit can lead to high voltage readings and trigger the P1838 code.

5. How do I diagnose the P1838 code on my 2015 GMC Sierra?

Start by inspecting the IMS wiring and connectors for damage or corrosion. Use a multimeter to check for proper voltage levels and test the IMS for functionality.

6. Can driving with the P1838 code damage my 2015 GMC Sierra?

Driving with this code can lead to further transmission issues or unsafe vehicle operation, so it's best to address the issue promptly.

7. How do I fix the P1838 code on a 2015 GMC Sierra?

Repairs may include replacing the Internal Mode Switch, repairing or replacing damaged wiring, cleaning corroded connections, or reprogramming the TCM if necessary.

8. Is the P1838 code specific to the 2015 GMC Sierra?

No, the P1838 code can occur in other vehicles equipped with similar transmission systems, but the exact diagnosis and repair steps may vary.

9. How much does it cost to fix the P1838 code on a 2015 GMC Sierra?

Repair costs depend on the root cause but can range from $150 to $500, including diagnostics, parts, and labor.

10. Can a bad Transmission Control Module (TCM) trigger the P1838 code?

Yes, a malfunctioning TCM could misinterpret voltage signals from the IMS, potentially causing the P1838 code.

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