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P18C3 2016 GMC Sierra Code - Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range

Quick Answer

The P18C3 diagnostic trouble code (DTC) for a 2016 GMC Sierra indicates that the Internal Mode Switch 'S' Circuit is stuck on an invalid voltage range. Common causes include Faulty Internal Mode Switch, Damaged wiring or connectors in the IMS circuit, Malfunctioning transmission control module. 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 2016 GMC Sierra indicates Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range.
Common causes
Common causes include Faulty Internal Mode Switch, Damaged wiring or connectors in the IMS circuit, Malfunctioning transmission control module.
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 Sep 16, 2024
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Code P18C3 2016 GMC Sierra Description

The P18C3 diagnostic trouble code (DTC) for a 2016 GMC Sierra indicates that the Internal Mode Switch 'S' Circuit is stuck on an invalid voltage range. The Internal Mode Switch (IMS) is a component within the transmission that communicates with the vehicle's onboard computer to determine the gear selection. The 'S' circuit refers to a specific circuit within the IMS that is responsible for detecting the gear selection. When the IMS 'S' circuit is stuck on an invalid voltage range, it means that the voltage signal being sent by the IMS is outside of the acceptable range, causing the vehicle's computer to detect an error.

OBDII Code P18C3 2016 GMC Sierra - Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range
P18C3 2016 GMC Sierra Code - Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range

Common Causes of P18C3 2016 GMC Sierra

  1. Faulty Internal Mode Switch
  2. Damaged wiring or connectors in the IMS circuit
  3. Malfunctioning transmission control module
  4. Corrosion or poor connections in the IMS circuit
  5. Electrical issues within the transmission system

Symptoms of P18C3 2016 GMC Sierra

  1. Erratic shifting behavior
  2. Transmission hesitation
  3. Stuck in a particular gear
  4. Poor acceleration
  5. Decreased fuel efficiency

How to Fix P18C3 2016 GMC Sierra

  1. Diagnose the specific cause of the issue using a scan tool to read the IMS voltage range and check for any fault codes.
  2. Inspect the wiring and connectors in the IMS circuit for any damage or corrosion. Repair or replace as necessary.
  3. Test the Internal Mode Switch for proper operation and replace if found to be faulty.
  4. Clear the DTC and perform a test drive to ensure the issue has been resolved.
  5. If the problem persists, further diagnostics may be required to identify any underlying transmission control module issues.

Cost to Fix P18C3 2016 GMC Sierra

The typical repair costs for addressing a P18C3 code on a 2016 GMC Sierra can vary depending on the specific cause of the issue. In general, replacing a faulty Internal Mode Switch can cost between $200 and $400, including parts and labor. However, if additional wiring repairs or module replacements are needed, the total repair cost could range from $300 to $800 or more. It's important to note that diagnosis time and labor rates at auto repair shops can vary, so it's advisable to check with local shops for a more accurate estimate based on your location and vehicle specifics.

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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 P18C3 2016 GMC Sierra Code

1. What does the OBDII code P18C3 mean on a 2016 GMC Sierra?

P18C3 refers to an issue with the Internal Mode Switch 'S' Circuit, indicating that the voltage in this circuit is stuck outside the acceptable range.

2. What are the common symptoms of a P18C3 code in a GMC Sierra?

Symptoms may include erratic shifting, the transmission being stuck in a specific gear, a check engine light, or reduced vehicle performance.

3. What causes the P18C3 code to appear on a 2016 GMC Sierra?

This code can be caused by a faulty internal mode switch, damaged wiring or connectors, a short or open circuit, or a problem with the transmission control module (TCM).

4. Can I drive my 2016 GMC Sierra with a P18C3 code?

While the vehicle may still be drivable, it is not recommended as it can lead to poor performance, further transmission damage, and unsafe driving conditions.

5. How do I diagnose the P18C3 code on a GMC Sierra?

Diagnosis involves checking the wiring and connectors for the internal mode switch, testing the switch itself, and using a scan tool to monitor voltage readings and other transmission data.

6. How do I fix the P18C3 code on my 2016 GMC Sierra?

Repairs may include replacing the internal mode switch, repairing or replacing damaged wiring or connectors, or reprogramming or replacing the transmission control module.

7. Is the internal mode switch part of the transmission on a GMC Sierra?

Yes, the internal mode switch is located within the transmission and communicates gear selection information to the transmission control module.

8. What tools are needed to troubleshoot the P18C3 code?

You’ll need a diagnostic scan tool capable of reading live data, a multimeter to test electrical circuits, and potentially a transmission wiring diagram for reference.

9. Can a low battery cause the P18C3 code on a GMC Sierra?

A low battery or poor electrical connections can sometimes trigger transmission-related codes, so ensuring proper battery voltage and connections is a good first step.

10. How much does it cost to repair a P18C3 code on a 2016 GMC Sierra?

Repair costs vary depending on the exact issue, but replacing an internal mode switch can range from $200 to $600, while wiring repairs or TCM replacement can add to the expense.

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