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Engine-Codes – GMC – P18C2 2018 GMC Sierra

P18C2 2018 GMC Sierra Code - Internal Mode Switch 'P' Circuit Stuck On Invalid Voltage Range

Quick Answer

The diagnostic trouble code P18C2 for a 2018 GMC Sierra indicates an issue with the Internal Mode Switch 'P' Circuit being stuck on an invalid voltage range. Common causes include Faulty Internal Mode Switch, Wiring issues or shorts in the circuit, Corrosion or poor connections in the electrical system. 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 Internal Mode Switch, Wiring issues or shorts in the circuit, Corrosion or poor connections in the electrical system.
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 17, 2024
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Code P18C2 2018 GMC Sierra Description

The diagnostic trouble code P18C2 for a 2018 GMC Sierra indicates an issue with the Internal Mode Switch 'P' Circuit being stuck on an invalid voltage range. The Internal Mode Switch (IMS) is a component within the transmission that communicates with the vehicle's control module to determine the gear selection. In this case, the circuit associated with the 'P' (Park) position is reporting a voltage that is outside of the acceptable range, which can lead to various performance issues.

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

Common Causes of P18C2 2018 GMC Sierra

  1. Faulty Internal Mode Switch
  2. Wiring issues or shorts in the circuit
  3. Corrosion or poor connections in the electrical system
  4. Issues with the vehicle's control module
  5. Environmental factors such as water intrusion or debris affecting the IMS

Symptoms of P18C2 2018 GMC Sierra

  1. Erratic shifting behavior
  2. Transmission slipping
  3. Difficulty starting the vehicle
  4. Inaccurate gear display on the dashboard
  5. Malfunctioning cruise control system

How to Fix P18C2 2018 GMC Sierra

  1. Begin by conducting a thorough inspection of the Internal Mode Switch and associated wiring to identify any visible damage or corrosion.
  2. Test the voltage output of the IMS 'P' Circuit to determine if it falls within the acceptable range specified by the manufacturer.
  3. Replace the Internal Mode Switch if it is found to be faulty or not functioning correctly.
  4. Repair any damaged wiring or connections in the circuit to ensure proper electrical flow.
  5. Clear the diagnostic trouble codes from the vehicle's system and perform a test drive to verify that the issue has been resolved.

Cost to Fix P18C2 2018 GMC Sierra

The typical repair costs for addressing the P18C2 code on a 2018 GMC Sierra can vary depending on the extent of the issue and the specific parts and labor required. In general, the cost of replacing the Internal Mode Switch and addressing any wiring issues can range from $200 to $500. Additional costs may apply if other components need to be replaced or if extensive diagnostic testing is required. It is advisable to consult with a qualified mechanic or auto repair shop to obtain a more accurate estimate based on the specific circumstances of the vehicle. Labor rates at auto repair shops typically range from $80 to $150 per hour, but can vary based on location and other factors.

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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.

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