AutoCodes – GMC – P1840 2014 GMC Sierra

P1840 2014 GMC Sierra Code - Internal Mode Switch 'S' Circuit Low 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: P1840 2014 GMC Sierra indicates Internal Mode Switch 'S' Circuit Low 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 178

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 P1840 2014 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 S signal circuit voltage is less than 0.7 V, for 1.75 s.

OBDII Code P1840 2014 GMC Sierra - Internal Mode Switch 'S' Circuit Low Voltage - AutoCodes.com — P1840 2014 GMC Sierra Code - Internal Mode Switch 'S' Circuit Low Voltage

What does this mean?

What are the Possible Causes of the DTC P1840 2014 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 P1840 2014 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 P1840 2014 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 P1840 2014 GMC Sierra code?

Need more information on how to fix the P1840 2014 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 P1840 2014 GMC Sierra Code

What are the common symptoms of OBDII code P1840 in a 2014 GMC Sierra?

Some common symptoms of OBDII code P1840 in a 2014 GMC Sierra include issues with shifting gears, hesitation during acceleration, and the inability to shift out of park.

What are the possible causes of the Internal Mode Switch 'S' Circuit Low Voltage code in a 2014 GMC Sierra?

Possible causes of OBDII code P1840 in a 2014 GMC Sierra include a faulty internal mode switch, damaged wiring or connectors related to the switch, or issues with the transmission control module.

How can I diagnose the Internal Mode Switch 'S' Circuit Low Voltage issue in my 2014 GMC Sierra?

Diagnosing OBDII code P1840 in a 2014 GMC Sierra may involve using a scan tool to retrieve the error code, checking the wiring and connectors related to the internal mode switch, and testing the switch itself for proper operation.

What are the repair options for fixing the Internal Mode Switch 'S' Circuit Low Voltage problem in a 2014 GMC Sierra?

Repair options for OBDII code P1840 in a 2014 GMC Sierra may include repairing or replacing damaged wiring or connectors, replacing the internal mode switch if faulty, or reprogramming the transmission control module.

Can I continue driving my 2014 GMC Sierra with OBDII code P1840?

It is not recommended to continue driving a 2014 GMC Sierra with OBDII code P1840, as it can lead to further damage to the transmission and affect the vehicle's drivability.

Is it possible to reset the OBDII code P1840 in a 2014 GMC Sierra without fixing the underlying issue?

While it is possible to reset the OBDII code P1840 in a 2014 GMC Sierra using a scan tool, the issue causing the code will likely persist and trigger the code again unless properly diagnosed and repaired.

How much does it typically cost to repair OBDII code P1840 in a 2014 GMC Sierra?

The cost of repairing OBDII code P1840 in a 2014 GMC Sierra can vary depending on the exact cause of the issue, but it may range from a few hundred to a few thousand dollars, including parts and labor.

Can a DIY enthusiast fix the Internal Mode Switch 'S' Circuit Low Voltage problem in a 2014 GMC Sierra?

While some DIY enthusiasts may be able to diagnose and repair OBDII code P1840 in a 2014 GMC Sierra, it is recommended to have the issue addressed by a qualified mechanic or technician due to the complexity of transmission-related repairs.