AutoCodes – GMC – P18B7 2015 GMC Sierra

P18B7 2015 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 2015 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 160

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 2015 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 2015 GMC Sierra - Internal Mode Switch 'C' Circuit Shorted - AutoCodes.com — P18B7 2015 GMC Sierra Code - Internal Mode Switch 'C' Circuit Shorted

What does this mean?

What are the Possible Causes of the DTC P18B7 2015 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 2015 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 2015 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 2015 GMC Sierra code?

Need more information on how to fix the P18B7 2015 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 2015 GMC Sierra Code

1. What does the OBDII code P18B7 mean on a 2015 GMC Sierra?

The P18B7 code indicates that the Internal Mode Switch 'C' circuit has a short, which is part of the transmission control system responsible for monitoring gear selection.

2. What are the common symptoms of the P18B7 code in a 2015 GMC Sierra?

Symptoms may include the transmission not shifting properly, erratic gear changes, the vehicle being stuck in one gear, or the check engine light being illuminated.

3. What causes the P18B7 code to appear on a 2015 GMC Sierra?

The main causes include damaged wiring or connectors in the Internal Mode Switch 'C' circuit, a faulty internal mode switch, or issues with the transmission control module (TCM).

4. Can a P18B7 code cause serious damage to my 2015 GMC Sierra?

While it may not cause immediate damage, driving with this code can lead to transmission issues, reduced performance, and potential long-term wear if not addressed.

5. How do I diagnose the P18B7 code on my 2015 GMC Sierra?

Use an OBDII scanner to confirm the code, inspect the wiring and connectors for damage, and test the internal mode switch and related circuits for continuity and shorts.

6. How do I fix the P18B7 code on a 2015 GMC Sierra?

Repairs may involve replacing damaged wiring or connectors, repairing or replacing the internal mode switch, or reprogramming or replacing the transmission control module if necessary.

7. How much does it cost to fix a P18B7 code on a 2015 GMC Sierra?

Repair costs vary depending on the issue but typically range from $100 to $400 for wiring repairs, while replacing the internal mode switch or TCM can cost $500 or more.

8. Can I drive my 2015 GMC Sierra with the P18B7 code active?

Itâ€™s not recommended, as the code may cause transmission performance issues, making the vehicle unsafe to drive and potentially causing further damage.

9. Will clearing the P18B7 code fix the problem on my 2015 GMC Sierra?

Clearing the code may temporarily turn off the check engine light, but the underlying issue must be repaired to prevent the code from returning.

10. Do I need a professional mechanic to fix the P18B7 code?

While minor wiring issues can sometimes be resolved by experienced DIYers, diagnosing and repairing internal mode switch or TCM issues typically requires a professional mechanic.