AutoCodes – GMC – P18B7 2018 GMC Sierra

P18B7 2018 GMC Sierra Code - Internal Mode Switch 'C' 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: P18B7 2018 GMC Sierra indicates Internal Mode Switch 'C' 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 224

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 P18B7 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 C signal circuit voltage is between 0.966–1.68 V, for 1.75 s.

OBDII Code P18B7 2018 GMC Sierra - Internal Mode Switch 'C' Circuit Shorted - AutoCodes.com — P18B7 2018 GMC Sierra Code - Internal Mode Switch 'C' Circuit Shorted

What does this mean?

What are the Possible Causes of the DTC P18B7 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 P18B7 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 P18B7 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 P18B7 2018 GMC Sierra code?

Need more information on how to fix the P18B7 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 P18B7 2018 GMC Sierra Code

1. What are common symptoms of OBDII code P18B7 in a 2018 GMC Sierra?

The common symptoms of OBDII code P18B7 (Internal Mode Switch 'C' Circuit Shorted) in a 2018 GMC Sierra may include issues with the transmission shifting erratically, difficulty shifting gears, and the transmission staying in one gear.

2. What can cause the Internal Mode Switch 'C' Circuit Shorted code in a 2018 GMC Sierra?

The Internal Mode Switch 'C' Circuit Shorted code (P18B7) in a 2018 GMC Sierra can be caused by a faulty internal mode switch, damaged wiring or connectors in the circuit, or a malfunctioning transmission control module.

3. How serious is the Internal Mode Switch 'C' Circuit Shorted code in a 2018 GMC Sierra?

The Internal Mode Switch 'C' Circuit Shorted code (P18B7) in a 2018 GMC Sierra should be addressed promptly as it can lead to transmission issues, affecting the vehicle's drivability and potentially causing further damage to the transmission system.

4. Can I continue driving my 2018 GMC Sierra with the P18B7 code?

It is not recommended to continue driving your 2018 GMC Sierra with the Internal Mode Switch 'C' Circuit Shorted code (P18B7) as it can result in transmission problems and potential safety hazards. It is best to have the issue diagnosed and repaired by a qualified mechanic.

5. How can I diagnose and repair the Internal Mode Switch 'C' Circuit Shorted code in my 2018 GMC Sierra?

Diagnosing and repairing the Internal Mode Switch 'C' Circuit Shorted code (P18B7) in a 2018 GMC Sierra typically involves checking the internal mode switch, inspecting the wiring and connectors for damage, and testing the transmission control module for faults. It is recommended to seek professional assistance for an accurate diagnosis and repair.

6. Is the Internal Mode Switch 'C' Circuit Shorted a common issue in 2018 GMC Sierra vehicles?

While the Internal Mode Switch 'C' Circuit Shorted code (P18B7) may not be extremely common, it can still occur in 2018 GMC Sierra vehicles due to various factors such as wear and tear, electrical issues, or component failures.

7. Can resetting the OBDII code P18B7 in my 2018 GMC Sierra fix the issue?

Simply resetting the OBDII code P18B7 (Internal Mode Switch 'C' Circuit Shorted) in your 2018 GMC Sierra may temporarily clear the warning light, but it will not fix the underlying problem causing the code. It is essential to diagnose and address the root cause of the issue for a permanent solution.

8. How much does it cost to repair the Internal Mode Switch 'C' Circuit Shorted code in a 2018 GMC Sierra?

The cost of repairing the Internal Mode Switch 'C' Circuit Shorted code (P18B7) in a 2018 GMC Sierra can vary depending on the extent of the issue, parts needed for replacement, and labor costs. It is advisable to obtain quotes from reputable repair shops for an accurate estimate.

9. Can a DIY enthusiast fix the Internal Mode Switch 'C' Circuit Shorted code in a 2018 GMC Sierra?

While some DIY enthusiasts may have the skills to diagnose and repair the Internal Mode Switch 'C' Circuit Shorted code (P18B7) in a 2018 GMC Sierra, it is a complex issue related to the transmission system. It is recommended to consult a professional mechanic for proper diagnosis and repair.

10. How long does it take to repair the Internal Mode Switch 'C' Circuit Shorted code in a 2018 GMC Sierra?

The repair time for the Internal Mode Switch 'C' Circuit Shorted code (P18B7) in a 2018 GMC Sierra can vary depending on the exact cause of the issue, availability of parts, and the mechanic's expertise. It may take a few hours to a full day to diagnose and repair the problem.