AutoCodes – Chevrolet – P1840 2016 Chevrolet Silverado

P1840 2016 Chevrolet Silverado 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 2016 Chevrolet Silverado 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 276

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 2016 Chevrolet Silverado 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 2016 Chevrolet Silverado - Internal Mode Switch 'S' Circuit Low Voltage - AutoCodes.com — P1840 2016 Chevrolet Silverado Code - Internal Mode Switch 'S' Circuit Low Voltage

What does this mean?

What are the Possible Causes of the DTC P1840 2016 Chevrolet Silverado?

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 2016 Chevrolet Silverado?

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 2016 Chevrolet Silverado 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 2016 Chevrolet Silverado code?

Need more information on how to fix the P1840 2016 Chevrolet Silverado 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 2016 Chevrolet Silverado Code

What does the OBDII code P1840 mean on a 2016 Chevrolet Silverado?

The P1840 code indicates an issue with the Internal Mode Switch (IMS) 'S' circuit, specifically low voltage detected by the transmission control module (TCM).

What are the common symptoms of the P1840 code in a 2016 Chevrolet Silverado?

Symptoms may include the Check Engine Light being illuminated, erratic or hard shifting, transmission stuck in one gear, or a failure to engage gears properly.

What causes the P1840 code to appear on a 2016 Chevrolet Silverado?

Common causes include a faulty Internal Mode Switch, wiring issues such as damaged or corroded connectors, a malfunctioning transmission control module, or low transmission fluid.

How can I diagnose the P1840 code on my 2016 Chevrolet Silverado?

Diagnose the issue by scanning for codes, inspecting IMS wiring and connectors for damage or corrosion, checking transmission fluid levels, and testing the IMS circuit with a multimeter.

Can I drive my 2016 Chevrolet Silverado with a P1840 code?

While it might be possible to drive, it is not recommended as the issue can lead to further transmission damage or unsafe driving conditions due to gear engagement problems.

How do I fix the P1840 code on a 2016 Chevrolet Silverado?

Repairs may include replacing the Internal Mode Switch, repairing or replacing damaged wiring or connectors, refilling or flushing transmission fluid, or reprogramming the TCM if necessary.

How much does it cost to repair a P1840 code on a 2016 Chevrolet Silverado?

The cost varies depending on the repair but can range from $150 to $400 for diagnostics and IMS replacement, with additional costs for wiring repairs or TCM programming.

Can a low battery voltage cause the P1840 code in a 2016 Chevrolet Silverado?

Yes, low battery voltage can cause improper TCM operation and trigger the P1840 code, so ensure the battery and charging system are functioning correctly.

Is the P1840 code specific to Chevrolet Silverado trucks?

No, the P1840 code can appear on other vehicles with similar drivetrain systems, but the details of the repair may vary by make and model.

How can I prevent the P1840 code from reoccurring on my 2016 Chevrolet Silverado?

Regularly inspect and maintain the transmission system, ensure proper fluid levels, and address wiring or electrical issues promptly to prevent future occurrences.