AutoCodes – GMC – P18C3 2014 GMC Sierra

P18C3 2014 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 2014 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 174

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 2014 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 2014 GMC Sierra - Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range - AutoCodes.com — P18C3 2014 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 2014 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 2014 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 2014 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 2014 GMC Sierra code?

Need more information on how to fix the P18C3 2014 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 2014 GMC Sierra Code

1. What does the OBDII code P18C3 mean on a 2014 GMC Sierra?

The code P18C3 indicates that the Internal Mode Switch 'S' Circuit is stuck on an invalid voltage range, which means the transmission control module (TCM) is detecting an issue with the range sensor circuit.

2. What are the common symptoms of code P18C3 in a 2014 GMC Sierra?

Symptoms may include the check engine light turning on, difficulty shifting gears, the transmission being stuck in one gear, or the vehicle going into limp mode.

3. What causes the P18C3 code to appear on a 2014 GMC Sierra?

Common causes include a faulty internal mode switch, damaged wiring or connectors in the mode switch circuit, a malfunctioning transmission control module (TCM), or electrical issues like short circuits or open circuits.

4. Can a bad transmission control module cause the P18C3 code?

Yes, a malfunctioning TCM can fail to properly interpret signals from the internal mode switch, potentially triggering the P18C3 code.

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

Diagnosis typically involves checking the wiring and connectors for damage, testing the internal mode switch for proper operation, and using a scan tool to monitor voltage readings in the circuit.

6. Can I drive my 2014 GMC Sierra with the P18C3 code?

Driving with the P18C3 code is not recommended, as it can lead to transmission issues like being stuck in gear or entering limp mode, which can compromise safety and cause further damage.

7. How do you fix the P18C3 code on a 2014 GMC Sierra?

Repairs may include replacing the internal mode switch, repairing or replacing damaged wiring or connectors in the circuit, and, in rare cases, replacing the transmission control module.

8. How much does it cost to fix the P18C3 code on a GMC Sierra?

Repair costs can vary, but replacing the internal mode switch typically costs between $150 and $400, while wiring repairs or TCM replacement may cost more depending on labor rates and part prices.

9. Can a weak battery cause the P18C3 code to appear?

A weak or failing battery can sometimes cause voltage-related issues, but itâ€™s not a common cause for this specific code. However, itâ€™s worth checking the battery and charging system during diagnosis.

10. Is the P18C3 code specific to the 2014 GMC Sierra?

No, the P18C3 code can appear on other GMC or Chevy vehicles with similar transmission systems, but the exact symptoms and repairs may vary slightly depending on the model and year.