AutoCodes – GMC – P1838 2018 GMC Sierra

P1838 2018 GMC Sierra Code - Internal Mode Switch 'A' Circuit High 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: P1838 2018 GMC Sierra indicates Internal Mode Switch 'A' Circuit High 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 196

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 P1838 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 A signal circuit voltage is greater than 2.38 V, for 1.75 s.

OBDII Code P1838 2018 GMC Sierra - Internal Mode Switch 'A' Circuit High Voltage - AutoCodes.com — P1838 2018 GMC Sierra Code - Internal Mode Switch 'A' Circuit High Voltage

What does this mean?

What are the Possible Causes of the DTC P1838 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 P1838 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 P1838 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 P1838 2018 GMC Sierra code?

Need more information on how to fix the P1838 2018 GMC Sierra code? Get Access to Factory Service Manuals

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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 2018 GMC Sierra Code

1. What are the common symptoms of OBDII code P1838 in a 2018 GMC Sierra?

The common symptoms of OBDII code P1838 in a 2018 GMC Sierra include issues with shifting gears, hesitation or jerking during acceleration, and the transmission getting stuck in a particular gear.

2. What causes the Internal Mode Switch 'A' Circuit High Voltage code (P1838) in a 2018 GMC Sierra?

The P1838 code in a 2018 GMC Sierra is typically caused by a malfunction in the internal mode switch, which detects the position of the gear shift lever and sends signals to the transmission control module.

3. How can I diagnose the Internal Mode Switch issue triggering code P1838 in my 2018 GMC Sierra?

Diagnosing the Internal Mode Switch issue causing code P1838 involves checking the wiring and connections related to the internal mode switch, testing the switch itself for proper functioning, and inspecting the transmission control module for any faults.

4. Can a faulty battery or electrical system cause OBDII code P1838 in a 2018 GMC Sierra?

Yes, a weak battery or an issue with the electrical system can potentially trigger the P1838 code in a 2018 GMC Sierra by causing voltage irregularities that affect the internal mode switch operation.

5. What are the repair options for fixing OBDII code P1838 in a 2018 GMC Sierra?

Repair options for addressing code P1838 in a 2018 GMC Sierra may include replacing the internal mode switch, repairing wiring or connections related to the switch, resetting the transmission control module, and ensuring the battery and electrical system are functioning correctly.

6. Can driving with OBDII code P1838 in a 2018 GMC Sierra cause further damage?

Continuing to drive with code P1838 in a 2018 GMC Sierra can potentially lead to transmission issues, poor fuel efficiency, and further damage to the internal mode switch or transmission control module if the underlying problem is not addressed promptly.

7. Is it safe to clear the P1838 trouble code in a 2018 GMC Sierra without performing repairs?

Clearing the P1838 trouble code in a 2018 GMC Sierra without addressing the underlying issue is not recommended, as the problem may persist and lead to ongoing transmission issues or trigger the check engine light again in the future.

8. How much does it typically cost to repair OBDII code P1838 in a 2018 GMC Sierra?

The cost of repairing OBDII code P1838 in a 2018 GMC Sierra can vary depending on the exact cause of the issue, the parts needed for repair, and labor costs. It is advisable to consult a professional mechanic for an accurate estimate.

9. Can a DIY enthusiast with automotive experience fix OBDII code P1838 in a 2018 GMC Sierra?

While some DIY enthusiasts may have the skills to diagnose and repair OBDII code P1838 in a 2018 GMC Sierra, dealing with transmission and electrical components can be complex. It is recommended to seek professional help for accurate diagnosis and repair.

10. How long does it take to repair OBDII code P1838 in a 2018 GMC Sierra?

The time required to repair OBDII code P1838 in a 2018 GMC Sierra can vary based on the exact issue, parts availability, and the expertise of the mechanic. It may take a few hours to a full day to complete the necessary repairs.