AutoCodes – GMC – P18B8 2018 GMC Sierra

P18B8 2018 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 2018 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 215

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 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 voltage is between 0.966–1.68 V, for 1.75 s.

OBDII Code P18B8 2018 GMC Sierra - Internal Mode Switch 'P' Circuit Shorted - AutoCodes.com — P18B8 2018 GMC Sierra Code - Internal Mode Switch 'P' Circuit Shorted

What does this mean?

What are the Possible Causes of the DTC P18B8 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 P18B8 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 P18B8 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 P18B8 2018 GMC Sierra code?

Need more information on how to fix the P18B8 2018 GMC Sierra code? Get Access to Factory Service Manuals

Need Help with the Code?

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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 2018 GMC Sierra Code

1. What are the common symptoms of OBDII code P18B8 on a 2018 GMC Sierra?

The common symptoms of OBDII code P18B8 include issues with shifting gears, difficulty starting the vehicle, and the inability to engage certain gears.

2. What causes the Internal Mode Switch 'P' Circuit Shorted code (P18B8) on a 2018 GMC Sierra?

The P18B8 code is typically caused by a short circuit in the internal mode switch 'P' circuit, which may be due to damaged wiring, a faulty internal mode switch, or a poor connection.

3. How can I diagnose the Internal Mode Switch 'P' Circuit Shorted code (P18B8) on my 2018 GMC Sierra?

Diagnosing the P18B8 code involves using a diagnostic scanner to retrieve the trouble codes, checking the internal mode switch for proper operation, inspecting the wiring for any damage, and testing the circuit for continuity.

4. Can I continue driving my 2018 GMC Sierra with the P18B8 trouble code?

It is not recommended to continue driving your vehicle with the P18B8 code present, as it can lead to further damage to the transmission or other components. It's best to address the issue promptly.

5. What are the repair options for fixing the Internal Mode Switch 'P' Circuit Shorted code (P18B8) on a 2018 GMC Sierra?

Repair options for the P18B8 code may include repairing or replacing damaged wiring, replacing the internal mode switch if faulty, ensuring proper connections, and clearing the trouble code from the vehicle's system.

6. How much does it typically cost to repair the P18B8 trouble code on a 2018 GMC Sierra?

The cost of repairing the P18B8 trouble code can vary depending on the extent of the damage and the specific repairs needed. It's recommended to consult a professional mechanic for an accurate estimate.

7. Can I reset the OBDII code P18B8 on my 2018 GMC Sierra by disconnecting the battery?

While disconnecting the battery may temporarily clear the trouble code, it is not a permanent solution. The underlying issue causing the P18B8 code needs to be properly diagnosed and repaired to prevent it from recurring.

8. Is the Internal Mode Switch 'P' Circuit Shorted code (P18B8) a common issue in 2018 GMC Sierra vehicles?

The P18B8 code may not be a common issue in 2018 GMC Sierra vehicles, but it can occur due to various factors such as wear and tear, electrical faults, or manufacturing defects.

9. Can a DIY enthusiast fix the Internal Mode Switch 'P' Circuit Shorted code (P18B8) on a 2018 GMC Sierra?

While some DIY enthusiasts may have the skills to diagnose and repair the P18B8 code, it's recommended to seek professional help, especially when dealing with transmission-related issues to ensure proper repair and safety.

10. How long does it take to repair the OBDII code P18B8 on a 2018 GMC Sierra?

The repair time for the P18B8 code can vary depending on the exact cause of the issue, the availability of parts, and the expertise of the mechanic. It may take a few hours to a full day to complete the repair.