AutoCodes – GMC – P18BF GMC

P18BF GMC 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 GMC 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 971

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

What does this mean?

What are the Possible Causes of the DTC P18BF GMC?

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 GMC?

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 GMC 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 GMC code?

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Need Help with the Code?

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Information for Specific GMC Models

P18BF 2014 GMC Sierra — Internal Mode Switch 'A' Circuit Stuck On Invalid Voltage Range
P18BF 2015 GMC Sierra — Internal Mode Switch 'A' Circuit Stuck On Invalid Voltage Range
P18BF 2016 GMC Sierra — Internal Mode Switch 'A' Circuit Stuck On Invalid Voltage Range
P18BF 2017 GMC Sierra — Internal Mode Switch 'A' Circuit Stuck On Invalid Voltage Range
P18BF 2018 GMC Sierra — Internal Mode Switch 'A' Circuit Stuck On Invalid Voltage Range

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 GMC Code

1. What are the common symptoms of OBDII code P18BF GMC?

The common symptoms of code P18BF GMC include issues with shifting gears, hesitation or jerking during acceleration, and the inability to start the vehicle.

2. What does the Internal Mode Switch 'A' Circuit Stuck On Invalid Voltage Range mean?

The code P18BF GMC indicates that the Internal Mode Switch 'A' circuit is stuck in an invalid voltage range, which can affect the proper operation of the transmission.

3. What are the possible causes of code P18BF GMC?

Possible causes of code P18BF GMC include a faulty internal mode switch, damaged wiring or connectors related to the internal mode switch, or issues with the transmission control module.

4. How can I diagnose OBDII code P18BF GMC?

Diagnosing code P18BF GMC typically involves using a scan tool to read the code, checking the wiring and connectors for any visible damage, and testing the internal mode switch for proper function.

5. Can I continue driving with OBDII code P18BF GMC?

It is not recommended to continue driving with code P18BF GMC as it can lead to further damage to the transmission system and potentially cause safety issues on the road.

6. How can I repair OBDII code P18BF GMC?

Repairing code P18BF GMC may involve replacing the internal mode switch, repairing or replacing damaged wiring or connectors, or reprogramming the transmission control module.

7. Is it possible to reset OBDII code P18BF GMC without fixing the underlying issue?

Resetting the code without fixing the underlying issue will only temporarily clear the code, and the problem is likely to return. It is important to diagnose and repair the root cause of the code.

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

While some DIY enthusiasts may be able to diagnose and repair code P18BF GMC, it is recommended to seek professional help, especially when dealing with transmission-related issues.

9. How much does it cost to fix OBDII code P18BF GMC?

The cost of fixing code P18BF GMC can vary depending on the root cause of the issue, the extent of the repairs needed, and the labor rates of the repair shop. It is advisable to get a professional estimate.

10. How can I prevent OBDII code P18BF GMC from occurring again?

To prevent OBDII code P18BF GMC from occurring again, it is essential to maintain regular transmission inspections, address any warning signs promptly, and follow the manufacturer's recommended maintenance schedule.