AutoCodes – GMC – P18C3 2016 GMC Sierra

P18C3 2016 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 2016 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 195

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 2016 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 2016 GMC Sierra - Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range - AutoCodes.com — P18C3 2016 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 2016 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 2016 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 2016 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 2016 GMC Sierra code?

Need more information on how to fix the P18C3 2016 GMC Sierra 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 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?

Youâ€™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.