Engine-Codes.com
Engine-Codes – GMC – P18C3 2017 GMC Sierra

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

Quick Answer

The P18C3 code indicates that the Internal Mode Switch 'S' Circuit is stuck on an invalid voltage range in a 2017 GMC Sierra. Common causes include Faulty internal mode switch that may be stuck or malfunctioning, Damaged or corroded wiring and connectors related to the mode switch, Issues within the transmission control module (TCM) itself. 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 internal mode switch that may be stuck or malfunctioning, Damaged or corroded wiring and connectors related to the mode switch, Issues within the transmission control module (TCM) itself.
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 Oct 17, 2024
💬 Need more help? Ask Auto Expert for instant answers — it's free!
AutoCodes App

Fix Your Car Smarter

Try the New AutoCodes App!

Get complete OBDII diagnostics, repair solutions, and cost estimates, plus AI chat support on demand.

AutoCodes App on Google Play

Code P18C3 2017 GMC Sierra Description

The P18C3 code indicates that the Internal Mode Switch 'S' Circuit is stuck on an invalid voltage range in a 2017 GMC Sierra. This code is primarily associated with the vehicle's transmission control module (TCM) and its ability to interpret signals from the mode switch. The mode switch is responsible for selecting different driving modes, such as normal, sport, or tow/haul, which can significantly affect the vehicle's performance and drivability. When the TCM detects that the voltage from the mode switch is outside the expected range, it triggers this diagnostic trouble code.

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

Common Causes of P18C3 2017 GMC Sierra

  1. Faulty internal mode switch that may be stuck or malfunctioning.
  2. Damaged or corroded wiring and connectors related to the mode switch.
  3. Issues within the transmission control module (TCM) itself.
  4. Poor electrical connections due to moisture or dirt ingress.
  5. Software glitches or programming issues within the TCM.

Symptoms of P18C3 2017 GMC Sierra

  1. Erratic or harsh shifting of the transmission.
  2. Inability to switch between driving modes (e.g., normal, sport).
  3. Activation of the check engine light or transmission warning light.
  4. Reduced engine performance or acceleration issues.
  5. Transmission may enter limp mode, restricting speed and power.

How to Fix P18C3 2017 GMC Sierra

  1. Diagnostic Scan: Begin by using an OBD-II scanner to confirm the P18C3 code and check for any additional codes that may provide more context.
  2. Visual Inspection: Inspect the wiring and connectors associated with the internal mode switch for any signs of damage, corrosion, or loose connections.
  3. Test the Mode Switch: Using a multimeter, test the mode switch to ensure it is functioning correctly and providing the expected voltage signals to the TCM.
  4. Repair or Replace Components: If the mode switch is faulty, replace it. If wiring issues are found, repair or replace the damaged sections as needed.
  5. Reprogram or Reset TCM: After repairs, it may be necessary to reprogram or reset the TCM to ensure it recognizes the new components and operates correctly.

Cost to Fix P18C3 2017 GMC Sierra

The typical repair costs for addressing the P18C3 code can range from $200 to $800, depending on the specific repairs needed. This estimate includes parts such as a new mode switch, wiring harnesses, and labor costs. Labor rates can vary significantly based on location, vehicle make and model, and engine type. Most auto repair shops charge between $80 and $150 per hour; however, rates in metropolitan areas or at dealerships may be higher, while independent shops often charge less. It is advisable to check local rates for a more precise estimate before proceeding with repairs.

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.

Discuss the causes and fixes for P18C3 2017 GMC Sierra OBDII Code

Submit a New Comment

Code P18C3 2017 GMC Sierra comments

No comments found for this page.