AutoCodes – GMC – P18C3 2017 GMC Sierra

P18C3 2017 GMC Sierra Code - Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range

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: P18C3 2017 GMC Sierra indicates Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range.
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 155

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 P18C3 2017 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 has an internal mode switch S signal circuit has an invalid voltage range of 0.70 – 0.96 V, for 2.7 s.

OBDII Code P18C3 2017 GMC Sierra - Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range - AutoCodes.com — P18C3 2017 GMC Sierra Code - Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range

What does this mean?

What are the Possible Causes of the DTC P18C3 2017 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 P18C3 2017 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 P18C3 2017 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 P18C3 2017 GMC Sierra code?

Need more information on how to fix the P18C3 2017 GMC Sierra code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P18C3 2017 GMC Sierra code diagnosed by a professional: Find a repair shop in your area

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 P18C3 2017 GMC Sierra Code

1. What are the common symptoms of OBDII code P18C3 in a 2017 GMC Sierra?

The common symptoms include issues with shifting gears, hesitation or jerking during acceleration, and the inability to start the vehicle.

2. What does the Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range mean in relation to the P18C3 code?

This means that there is a problem with the voltage range detected in the internal mode switch 'S' circuit, which is responsible for communicating gear position to the vehicle's computer.

3. What are the possible causes of the Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range code in a 2017 GMC Sierra?

Possible causes include a faulty internal mode switch, damaged wiring or connectors in the circuit, low transmission fluid level, or a malfunctioning transmission control module.

4. How can I diagnose the cause of the P18C3 code in my 2017 GMC Sierra?

You can use a diagnostic scanner to read the OBDII code and further investigate the internal mode switch, wiring, and connectors for any visible damage or issues. It's recommended to consult a professional mechanic for a thorough diagnosis.

5. Can I drive my 2017 GMC Sierra with the P18C3 code present?

It is not recommended to drive your vehicle with the P18C3 code present, as it can lead to further damage to the transmission system and potentially unsafe driving conditions.

6. How can I repair the Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range issue in my 2017 GMC Sierra?

Repair options may include replacing the internal mode switch, repairing or replacing damaged wiring and connectors, checking and topping up transmission fluid, or reprogramming the transmission control module.

7. Is the P18C3 code a serious issue that requires immediate attention?

Yes, the P18C3 code is a serious issue that should be addressed promptly to prevent further damage to the transmission system and ensure the safety and performance of your 2017 GMC Sierra.

8. Can a DIY enthusiast fix the P18C3 code in a 2017 GMC Sierra?

While some basic troubleshooting steps can be done by a DIY enthusiast, it is recommended to seek professional help for diagnosing and repairing the Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range issue to ensure proper and effective resolution.

9. How much does it typically cost to repair the P18C3 code in a 2017 GMC Sierra?

The cost of repairing the P18C3 code can vary depending on the underlying cause of the issue, the parts needed for repair, and the labor costs. It's best to get a quote from a trusted mechanic or dealership for an accurate estimate.

10. Will resetting the OBDII code clear the P18C3 issue in my 2017 GMC Sierra?

Resetting the OBDII code may temporarily clear the P18C3 code, but it will not fix the underlying issue causing the Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range problem. It's important to diagnose and repair the root cause of the code for a permanent solution.