AutoCodes – GMC – P18B5 2015 GMC Sierra

P18B5 2015 GMC Sierra Code - Internal Mode Switch 'A' 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: P18B5 2015 GMC Sierra indicates Internal Mode Switch 'A' 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 273

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 P18B5 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 A signal circuit voltage is between 0.966–1.68 V, for 1.75 s.

OBDII Code P18B5 2015 GMC Sierra - Internal Mode Switch 'A' Circuit Shorted - AutoCodes.com — P18B5 2015 GMC Sierra Code - Internal Mode Switch 'A' Circuit Shorted

What does this mean?

What are the Possible Causes of the DTC P18B5 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 P18B5 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 P18B5 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 P18B5 2015 GMC Sierra code?

Need more information on how to fix the P18B5 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 P18B5 2015 GMC Sierra Code

What does the OBDII code P18B5 mean on a 2015 GMC Sierra?

1. P18B5 indicates that the Internal Mode Switch 'A' circuit in the transmission system has a short, which impacts the vehicle's ability to correctly detect gear positions. 2.

What are the common symptoms of code P18B5 in a 2015 GMC Sierra?

Symptoms may include difficulty shifting gears, the transmission being stuck in one gear, erratic shifting, or the transmission going into limp mode. 3.

What causes the P18B5 code to appear on a 2015 GMC Sierra?

Common causes include damaged wiring or connectors in the Internal Mode Switch 'A' circuit, a faulty Internal Mode Switch, or a shorted circuit. 4.

Can driving with the P18B5 code damage my 2015 GMC Sierra?

Yes, driving with this code can cause further damage to the transmission system and may result in unsafe driving conditions due to erratic shifting. 5.

How can I diagnose the P18B5 code on my 2015 GMC Sierra?

Use an OBDII scanner to verify the code, inspect the wiring and connectors for damage, and test the Internal Mode Switch for proper operation. 6.

What is the Internal Mode Switch in a 2015 GMC Sierra?

The Internal Mode Switch is a component in the transmission that communicates the gear position to the vehicleâ€™s computer system. 7.

How do I fix the P18B5 code on a 2015 GMC Sierra?

Repairs may include replacing damaged wiring, repairing or replacing connectors, or replacing a faulty Internal Mode Switch. 8.

Is the P18B5 code specific to GMC vehicles?

No, the code can appear on other vehicles as well, but its meaning and repair process may vary depending on the make and model. 9.

How much does it cost to repair the P18B5 code on a 2015 GMC Sierra?

Repair costs vary depending on the issue but typically range from $150 to $500, with higher costs if the Internal Mode Switch needs replacement. 10.

Can I fix the P18B5 code on my 2015 GMC Sierra myself?

If you have experience with automotive electrical systems, you can inspect and repair wiring or connectors, but replacing the Internal Mode Switch may require professional assistance.