AutoCodes – GMC – P18B8 2016 GMC Sierra

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

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: P18B8 2016 GMC Sierra indicates Internal Mode Switch 'P' Circuit Shorted.
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 187

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 P18B8 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 the internal mode switch P signal circuit voltage is between 0.966–1.68 V, for 1.75 s.

OBDII Code P18B8 2016 GMC Sierra - Internal Mode Switch 'P' Circuit Shorted - AutoCodes.com — P18B8 2016 GMC Sierra Code - Internal Mode Switch 'P' Circuit Shorted

What does this mean?

What are the Possible Causes of the DTC P18B8 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 P18B8 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 P18B8 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 P18B8 2016 GMC Sierra code?

Need more information on how to fix the P18B8 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 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.