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P18B8 2016 GMC Sierra Code - Internal Mode Switch 'P' Circuit Shorted

Quick Answer

The diagnostic trouble code P18B8 for a 2016 GMC Sierra indicates an issue with the Internal Mode Switch 'P' Circuit being shorted. Common causes include Faulty Internal Mode Switch, Wiring harness issues, Corrosion or damage to electrical connectors. 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
P18B8 2016 GMC Sierra indicates Internal Mode Switch 'P' Circuit Shorted.
Common causes
Common causes include Faulty Internal Mode Switch, Wiring harness issues, Corrosion or damage to electrical connectors.
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 13, 2024
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Code P18B8 2016 GMC Sierra Description

The diagnostic trouble code P18B8 for a 2016 GMC Sierra indicates an issue with the Internal Mode Switch 'P' Circuit being shorted. The Internal Mode Switch (IMS) is a component of the transmission control system that helps the vehicle's computer determine the current gear selection. In this case, the 'P' circuit refers to the Park position. When the circuit is shorted, it means that there is an abnormal connection or low resistance in the circuit, which can disrupt the communication between the IMS and the vehicle's computer.

OBDII Code P18B8 2016 GMC Sierra - Internal Mode Switch 'P' Circuit Shorted
P18B8 2016 GMC Sierra Code - Internal Mode Switch 'P' Circuit Shorted

Common Causes of P18B8 2016 GMC Sierra

  1. Faulty Internal Mode Switch
  2. Wiring harness issues
  3. Corrosion or damage to electrical connectors
  4. Short circuit in the 'P' circuit
  5. Issues with the transmission control module

Symptoms of P18B8 2016 GMC Sierra

  1. Difficulty shifting into gear
  2. Vehicle stuck in Park or Neutral
  3. Transmission slipping or erratic shifting
  4. Limp mode activation
  5. Check Engine Light illuminated

How to Fix P18B8 2016 GMC Sierra

  1. Diagnose the specific cause of the shorted 'P' circuit using a diagnostic scanner and multimeter.
  2. Inspect the Internal Mode Switch and wiring harness for any visible damage or corrosion.
  3. Repair or replace any damaged wiring or connectors in the 'P' circuit.
  4. Replace the Internal Mode Switch if it is found to be faulty.
  5. Clear the trouble codes and perform a test drive to ensure the issue has been resolved.

Cost to Fix P18B8 2016 GMC Sierra

The typical repair costs for addressing a shorted 'P' circuit in a 2016 GMC Sierra can range from $200 to $500, depending on the specific cause of the issue and the cost of parts and labor. It's important to note that diagnosis time and labor rates at auto repair shops can vary, with hourly rates typically ranging from $80 to $150. Factors such as location, vehicle make and model, and engine type can also impact the final repair costs. It is advisable to consult with a trusted mechanic or repair shop for a more accurate estimate based on your specific circumstances.

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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 P18B8 2016 GMC Sierra Code

1. What are the common symptoms of the OBDII code P18B8 in a 2016 GMC Sierra?

The common symptoms of the P18B8 code include issues with shifting gears, hesitation when accelerating, and the vehicle not starting.

2. What does the OBDII code P18B8 'Internal Mode Switch P Circuit Shorted' mean for a 2016 GMC Sierra?

The P18B8 code indicates a problem with the internal mode switch circuit being shorted in a 2016 GMC Sierra, potentially affecting the transmission's operation.

3. What are the possible causes of the OBDII code P18B8 in a 2016 GMC Sierra?

Possible causes of the P18B8 code include a faulty internal mode switch, damaged wiring or connectors in the circuit, or a malfunctioning transmission control module.

4. How can I diagnose the OBDII code P18B8 in my 2016 GMC Sierra?

Diagnosing the P18B8 code involves using a diagnostic scanner to retrieve the code, inspecting the internal mode switch and its circuit for damage, and testing the transmission control module for proper function.

5. Is it safe to drive my 2016 GMC Sierra with the OBDII code P18B8 present?

It is not recommended to drive your vehicle with the P18B8 code present, as it can lead to further transmission issues and potentially cause unsafe driving conditions.

6. Can I repair the OBDII code P18B8 in my 2016 GMC Sierra myself?

While some DIY enthusiasts may attempt to address the P18B8 code themselves by checking wiring and connectors for damage, it is recommended to seek professional help for accurate diagnosis and repair.

7. How much does it typically cost to repair the OBDII code P18B8 in a 2016 GMC Sierra?

The cost of repairing the P18B8 code can vary depending on the root cause of the issue, but it may involve replacing the internal mode switch, repairing wiring, or reprogramming the transmission control module.

8. Will resetting the OBDII code P18B8 in my 2016 GMC Sierra make it go away permanently?

Resetting the P18B8 code may temporarily clear the error code, but if the underlying issue causing the code is not addressed, it is likely to reappear after driving the vehicle for a certain distance or time.

9. Can a faulty internal mode switch cause other OBDII codes to appear in a 2016 GMC Sierra?

Yes, a faulty internal mode switch can cause other related OBDII codes to appear, affecting the proper operation of the transmission and triggering additional error codes.

10. How important is it to address the OBDII code P18B8 promptly in a 2016 GMC Sierra?

It is crucial to address the P18B8 code promptly to prevent further damage to the transmission system, ensure safe driving conditions, and maintain the overall performance of the 2016 GMC Sierra.

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