AutoCodes – GMC – P18C2 2018 GMC Sierra

P18C2 2018 GMC Sierra Code - Internal Mode Switch 'P' 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: P18C2 2018 GMC Sierra indicates Internal Mode Switch 'P' 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 128

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 P18C2 2018 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 the internal mode switch P signal circuit has an invalid voltage range of 0.70 – 0.96 V for 2.7 s.

OBDII Code P18C2 2018 GMC Sierra - Internal Mode Switch 'P' Circuit Stuck On Invalid Voltage Range - AutoCodes.com — P18C2 2018 GMC Sierra Code - Internal Mode Switch 'P' Circuit Stuck On Invalid Voltage Range

What does this mean?

What are the Possible Causes of the DTC P18C2 2018 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 P18C2 2018 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 P18C2 2018 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 P18C2 2018 GMC Sierra code?

Need more information on how to fix the P18C2 2018 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 P18C2 2018 GMC Sierra Code

1. What are the common symptoms of OBDII code P18C2 in a 2018 GMC Sierra?

The common symptoms of OBDII code P18C2 include issues with the transmission shifting smoothly, difficulty selecting gears, and illumination of the Check Engine light on the dashboard.

2. What does the OBDII code P18C2 'Internal Mode Switch 'P' Circuit Stuck On Invalid Voltage Range' indicate in a 2018 GMC Sierra?

The OBDII code P18C2 indicates that the internal mode switch 'P' circuit in the transmission control module is stuck in an invalid voltage range, affecting the proper operation of the transmission.

3. What are the possible causes of OBDII code P18C2 in a 2018 GMC Sierra?

Possible causes of OBDII code P18C2 include a faulty internal mode switch, damaged wiring or connectors in the circuit, a malfunctioning transmission control module, or a software issue.

4. How can I diagnose OBDII code P18C2 in a 2018 GMC Sierra?

Diagnosing OBDII code P18C2 involves using a scan tool to retrieve the code, inspecting the internal mode switch and its circuit for any visible damage, testing the voltage range, and checking the wiring and connectors for proper connection.

5. What are the repair options for OBDII code P18C2 in a 2018 GMC Sierra?

Repair options for OBDII code P18C2 may include replacing the internal mode switch, repairing or replacing damaged wiring or connectors, reprogramming the transmission control module, or seeking professional help for further diagnosis and repair.

6. Can I continue driving my 2018 GMC Sierra with OBDII code P18C2?

It is not recommended to continue driving your 2018 GMC Sierra with OBDII code P18C2, as it can lead to further transmission issues and potential safety hazards. It is best to address the problem promptly.

7. How urgent is it to fix OBDII code P18C2 in a 2018 GMC Sierra?

It is advisable to address OBDII code P18C2 in a timely manner to prevent any further damage to the transmission system and ensure the proper operation of your 2018 GMC Sierra.

8. Can I reset OBDII code P18C2 in a 2018 GMC Sierra by disconnecting the battery?

While disconnecting the battery may clear the code temporarily, it is not a recommended long-term solution. The underlying issue causing OBDII code P18C2 needs to be diagnosed and repaired to prevent the code from reoccurring.

9. How much does it cost to repair OBDII code P18C2 in a 2018 GMC Sierra?

The cost of repairing OBDII code P18C2 in a 2018 GMC Sierra can vary depending on the specific cause of the issue, the parts needed for repair, and whether you choose to do the repair yourself or seek professional help.

10. Is OBDII code P18C2 covered under warranty for a 2018 GMC Sierra?

Whether OBDII code P18C2 is covered under warranty for a 2018 GMC Sierra depends on the specific terms of your vehicle's warranty. It is recommended to check with your dealership or refer to your warranty documentation for more information.