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P1838 2018 GMC Sierra Code - Internal Mode Switch 'A' Circuit High Voltage

Quick Answer

The P1838 diagnostic trouble code (DTC) for a 2018 GMC Sierra indicates an issue with the Internal Mode Switch 'A' Circuit High 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
P1838 2018 GMC Sierra indicates Internal Mode Switch 'A' Circuit High 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.
What is this?
Table of contents Created and updated by William Orellana on Sep 17, 2024
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Code P1838 2018 GMC Sierra Description

The P1838 diagnostic trouble code (DTC) for a 2018 GMC Sierra indicates an issue with the Internal Mode Switch 'A' Circuit High Voltage. This code is related to the transmission range selector switch, also known as the internal mode switch, which is responsible for communicating the gear selection to the vehicle's transmission control module (TCM). When the TCM detects a high voltage signal from the internal mode switch 'A' circuit, it triggers the P1838 code.

OBDII Code P1838 2018 GMC Sierra - Internal Mode Switch 'A' Circuit High Voltage
P1838 2018 GMC Sierra Code - Internal Mode Switch 'A' Circuit High Voltage

Common Causes of P1838 2018 GMC Sierra

  1. Faulty internal mode switch
  2. Damaged wiring or connectors in the circuit
  3. Malfunctioning TCM
  4. Software glitch in the transmission control system
  5. Corrosion or moisture in the electrical connections

Symptoms of P1838 2018 GMC Sierra

  1. Transmission slipping or hesitation
  2. Inability to shift gears smoothly
  3. Check Engine Light illuminated
  4. Harsh or delayed shifting
  5. Vehicle stuck in a particular gear

How to Fix P1838 2018 GMC Sierra

  1. Begin by conducting a thorough inspection of the internal mode switch, wiring, and connectors for any visible damage or corrosion.
  2. Use a multimeter to test the voltage output from the internal mode switch 'A' circuit to determine if it is within the specified range.
  3. If the voltage is too high, replace the internal mode switch and clear the DTC from the TCM memory.
  4. Check for any software updates for the TCM and perform a relearn procedure to ensure proper communication between the internal mode switch and the TCM.
  5. Test drive the vehicle to confirm that the transmission is shifting correctly and that the P1838 code does not reappear.

Cost to Fix P1838 2018 GMC Sierra

The typical repair costs for addressing the P1838 code on a 2018 GMC Sierra can vary depending on the exact cause of the issue. In general, replacing the internal mode switch and performing any necessary repairs to the wiring or connectors may cost between $200 and $500, including parts and labor. However, it is essential to note that specific diagnosis time and labor rates at auto repair shops can vary based on factors such as location, vehicle make and model, and engine type. It is advisable to check with local repair shops for a more accurate estimate based on your specific circumstances.

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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.

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