AutoCodes – GMC – P18BF 2015 GMC Sierra

P18BF 2015 GMC Sierra Code - Internal Mode Switch 'A' Circuit Stuck On Invalid Voltage Range

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: P18BF 2015 GMC Sierra indicates Internal Mode Switch 'A' Circuit Stuck On Invalid Voltage Range.
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 151

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 P18BF 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 has an invalid voltage range of 0.70 – 0.96 V, for 2.7 s.

OBDII Code P18BF 2015 GMC Sierra - Internal Mode Switch 'A' Circuit Stuck On Invalid Voltage Range - AutoCodes.com — P18BF 2015 GMC Sierra Code - Internal Mode Switch 'A' Circuit Stuck On Invalid Voltage Range

What does this mean?

What are the Possible Causes of the DTC P18BF 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 P18BF 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 P18BF 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 P18BF 2015 GMC Sierra code?

Need more information on how to fix the P18BF 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 P18BF 2015 GMC Sierra Code

1. What are the common symptoms of OBDII code P18BF on a 2015 GMC Sierra?

- Common symptoms include issues with shifting gears, the vehicle getting stuck in a particular gear, and the Check Engine light illuminating on the dashboard.

2. What does the OBDII code P18BF mean for a 2015 GMC Sierra?

- The code P18BF indicates a problem with the Internal Mode Switch 'A' Circuit being stuck on an invalid voltage range in the transmission control module.

3. What are the possible causes of OBDII code P18BF on a 2015 GMC Sierra?

- The potential causes of this code include a faulty internal mode switch, damaged wiring or connectors in the circuit, or issues with the transmission control module.

4. How can I diagnose the Internal Mode Switch 'A' Circuit issue causing code P18BF on my 2015 GMC Sierra?

- Diagnosing this issue typically involves using a scan tool to read the code, testing the internal mode switch for proper operation, and checking the wiring and connectors for any damage.

5. Can I continue driving my 2015 GMC Sierra with OBDII code P18BF present?

- It is not recommended to drive the vehicle with this code present, as it can lead to transmission issues and potential safety hazards on the road.

6. How can I repair OBDII code P18BF on my 2015 GMC Sierra?

- Repairing this code may involve replacing the internal mode switch, repairing any damaged wiring or connectors, or reprogramming the transmission control module.

7. Is it possible to reset OBDII code P18BF on a 2015 GMC Sierra without addressing the underlying issue?

- While clearing the code may temporarily turn off the Check Engine light, the underlying issue causing the code will persist until properly diagnosed and repaired.

8. Can a DIY enthusiast fix OBDII code P18BF on a 2015 GMC Sierra?

- Depending on their skill level and access to tools, a DIY enthusiast may be able to diagnose and repair this code, but it is recommended to seek professional help for complex transmission issues.

9. How much does it typically cost to repair OBDII code P18BF on a 2015 GMC Sierra at a repair shop?

- The cost of repairing this code can vary depending on the exact cause of the issue, but it may range from a few hundred to over a thousand dollars, including parts and labor.

10. Are there any preventive maintenance tips to avoid OBDII code P18BF on a 2015 GMC Sierra?

- Regularly servicing the transmission, checking for any signs of wiring damage, and addressing any shifting issues promptly can help prevent the occurrence of code P18BF.