AutoCodes – GMC – P1838 GMC

P1838 GMC 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 GMC 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 1,383

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

What does this mean?

What are the Possible Causes of the DTC P1838 GMC?

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 GMC?

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 GMC 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 GMC code?

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

Need Help with the Code?

Get the P1838 GMC code diagnosed by a professional: Find a repair shop in your area

Information for Specific GMC Models

P1838 2014 GMC Sierra — Internal Mode Switch 'A' Circuit High Voltage
P1838 2015 GMC Sierra — Internal Mode Switch 'A' Circuit High Voltage
P1838 2016 GMC Sierra — Internal Mode Switch 'A' Circuit High Voltage
P1838 2017 GMC Sierra — Internal Mode Switch 'A' Circuit High Voltage
P1838 2018 GMC Sierra — Internal Mode Switch 'A' Circuit High Voltage

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 GMC Code

1. What are the common symptoms of OBDII code P1838 GMC (Internal Mode Switch 'A' Circuit High Voltage)?

- Common symptoms include issues with shifting gears, erratic shifting patterns, and the transmission staying in one gear.

2. What are the possible causes of OBDII code P1838 GMC?

- The code P1838 can be triggered by a faulty internal mode switch, damaged wiring or connectors, or a malfunctioning transmission control module.

3. How can I diagnose OBDII code P1838 GMC?

- Diagnosis involves using a scan tool to read the code, checking the internal mode switch for proper operation, inspecting wiring and connectors for damage, and testing the transmission control module.

4. Can driving with OBDII code P1838 GMC cause further damage to the vehicle?

- Continuing to drive with code P1838 can lead to further transmission issues, including potential damage to the transmission components.

5. What are some repair tips for fixing OBDII code P1838 GMC?

- Repair tips include replacing the internal mode switch if it's faulty, repairing any damaged wiring or connectors, and reprogramming or replacing the transmission control module if necessary.

6. Is it safe to continue driving my vehicle with OBDII code P1838 GMC?

- It is not recommended to drive the vehicle with code P1838, as it can lead to transmission problems and potentially unsafe driving conditions.

7. Can I reset OBDII code P1838 GMC with a simple DIY method?

- While you can clear the code with a scan tool, it is important to diagnose and address the underlying issue to prevent the code from reoccurring.

8. How much does it typically cost to repair OBDII code P1838 GMC?

- The cost of repairing code P1838 can vary depending on the specific issue, but it may range from $200 to $800 or more, including parts and labor.

9. Are there any preventive measures to avoid OBDII code P1838 GMC in the future?

- Regular maintenance of the transmission system, such as fluid changes and inspections, can help prevent issues that may trigger code P1838.

10. Can a DIY enthusiast fix OBDII code P1838 GMC at home?

- Depending on the cause of the code, some DIY enthusiasts may be able to address the issue themselves, such as replacing the internal mode switch or repairing wiring, but more complex repairs may require professional assistance.