AutoCodes – GMC – P18B9 2014 GMC Sierra

P18B9 2014 GMC Sierra Code - Internal Mode Switch 'S' 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: P18B9 2014 GMC Sierra indicates Internal Mode Switch 'S' 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 141

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 P18B9 2014 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 S signal circuit voltage is between 0.966–1.68 V, for 1.75 s.

OBDII Code P18B9 2014 GMC Sierra - Internal Mode Switch 'S' Circuit Shorted - AutoCodes.com — P18B9 2014 GMC Sierra Code - Internal Mode Switch 'S' Circuit Shorted

What does this mean?

What are the Possible Causes of the DTC P18B9 2014 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 P18B9 2014 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 P18B9 2014 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 P18B9 2014 GMC Sierra code?

Need more information on how to fix the P18B9 2014 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 P18B9 2014 GMC Sierra Code

1. What does the OBDII code P18B9 mean on a 2014 GMC Sierra?

The P18B9 code indicates an issue with the Internal Mode Switch (IMS) 'S' circuit, specifically a shorted condition.

2. What are the common symptoms of code P18B9 on a 2014 GMC Sierra?

Symptoms may include difficulty shifting gears, the transmission stuck in a single gear, or the check engine light being illuminated.

3. What causes the P18B9 code to appear on a GMC Sierra?

Common causes include damaged wiring, a short circuit in the IMS 'S' circuit, a faulty internal mode switch, or issues within the transmission control module (TCM).

4. How can I diagnose the P18B9 code?

Start by inspecting the wiring and connectors for damage or corrosion, test the IMS circuit for continuity, and use a scan tool to confirm the fault and check for related codes.

5. Can I drive my 2014 GMC Sierra with a P18B9 code?

Driving with this code is not recommended as it can lead to transmission issues, limited gear operation, or further damage to the transmission system.

6. How do I fix the P18B9 code on a GMC Sierra?

Repairs may involve fixing or replacing damaged wiring, cleaning corroded connectors, or replacing a faulty internal mode switch.

7. How much does it cost to repair a P18B9 code?

The cost varies depending on the issue, but replacing the internal mode switch can range from $200 to $500, including parts and labor.

8. Is the P18B9 code related to the transmission in my GMC Sierra?

Yes, the P18B9 code specifically pertains to the transmission's internal mode switch and its associated circuitry.

9. What tools do I need to troubleshoot the P18B9 code?

Youâ€™ll need a diagnostic scan tool, a multimeter to check circuits, and possibly wiring diagrams for your vehicle.

10. Can a software update fix the P18B9 code?

In some cases, a software update for the transmission control module (TCM) may resolve the issue, but this is less common than physical repairs. Always consult a professional for a proper diagnosis.