AutoCodes – Chevrolet – P1840 2018 Chevrolet Silverado

P1840 2018 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 2018 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 285

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 2018 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 2018 Chevrolet Silverado - Internal Mode Switch 'S' Circuit Low Voltage - AutoCodes.com — P1840 2018 Chevrolet Silverado Code - Internal Mode Switch 'S' Circuit Low Voltage

What does this mean?

What are the Possible Causes of the DTC P1840 2018 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 2018 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 2018 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 2018 Chevrolet Silverado code?

Need more information on how to fix the P1840 2018 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 2018 Chevrolet Silverado Code

1. What are the common symptoms of OBDII code P1840 in a 2018 Chevrolet Silverado?

- Common symptoms include issues with shifting gears, difficulty starting the vehicle, and the transmission not engaging properly.

2. What does the Internal Mode Switch 'S' Circuit Low Voltage mean for a 2018 Chevrolet Silverado?

- This code indicates a problem with the internal mode switch, which is a component that helps the vehicle's computer system determine the gear position.

3. What are the possible causes of the Internal Mode Switch 'S' Circuit Low Voltage code in a 2018 Chevrolet Silverado?

- Potential causes include a faulty internal mode switch, damaged wiring or connectors, low transmission fluid levels, or issues with the transmission control module.

4. How can I diagnose the Internal Mode Switch 'S' Circuit Low Voltage issue in my 2018 Chevrolet Silverado?

- Diagnosis typically involves using a scan tool to retrieve the OBDII code, checking the internal mode switch and its connections, inspecting the wiring for damage, and testing the transmission fluid level.

5. Can I continue driving my 2018 Chevrolet Silverado with the P1840 code?

- It is not recommended to continue driving the vehicle with this code present, as it can lead to further transmission problems and potential safety issues.

6. How can I repair the Internal Mode Switch 'S' Circuit Low Voltage problem in my 2018 Chevrolet Silverado?

- Repair may involve replacing the internal mode switch, repairing any damaged wiring or connectors, ensuring proper transmission fluid levels, or reprogramming the transmission control module.

7. Is it possible to reset the OBDII code P1840 in a 2018 Chevrolet Silverado?

- The code can be reset using an OBDII scan tool after the underlying issue has been identified and repaired. However, if the problem persists, the code is likely to reappear.

8. How much does it typically cost to repair the Internal Mode Switch 'S' Circuit Low Voltage issue in a 2018 Chevrolet Silverado?

- The cost of repairs can vary depending on the specific cause of the problem and the extent of the damage, but it may range from a few hundred to a few thousand dollars.

9. Can a DIY enthusiast fix the P1840 code in a 2018 Chevrolet Silverado?

- While some basic diagnosis and repairs can be done by a DIY enthusiast, fixing the Internal Mode Switch 'S' Circuit Low Voltage issue may require specialized tools and expertise, so professional help is often recommended.

10. How can I prevent the recurrence of the P1840 code in my 2018 Chevrolet Silverado?

- Regular maintenance, such as checking transmission fluid levels, inspecting wiring connections, and promptly addressing any transmission issues, can help prevent the reoccurrence of this code.