AutoCodes – GMC – P18BF 2018 GMC Sierra

P18BF 2018 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 2018 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 156

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 2018 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 2018 GMC Sierra - Internal Mode Switch 'A' Circuit Stuck On Invalid Voltage Range - AutoCodes.com — P18BF 2018 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 2018 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 2018 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 2018 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 2018 GMC Sierra code?

Need more information on how to fix the P18BF 2018 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 2018 GMC Sierra Code

1. What are the common symptoms of OBDII code P18BF in a 2018 GMC Sierra?

The common symptoms of code P18BF include issues with shifting gears, erratic shifting patterns, and the vehicle being stuck in a particular gear.

2. What causes the Internal Mode Switch 'A' Circuit Stuck On Invalid Voltage Range in a 2018 GMC Sierra?

The P18BF code is typically triggered by a faulty internal mode switch, damaged wiring, or a poor connection within the circuit.

3. How can I diagnose the Internal Mode Switch 'A' Circuit issue in my 2018 GMC Sierra?

Diagnosing this issue involves using a scan tool to retrieve the trouble codes, conducting a visual inspection of the wiring, and performing voltage tests on the internal mode switch.

4. Can a DIY enthusiast repair the P18BF code in a 2018 GMC Sierra?

While some experienced DIYers may be able to address this issue by replacing the internal mode switch or repairing the wiring, it is recommended to seek professional help for accurate diagnosis and repair.

5. Is it safe to continue driving my 2018 GMC Sierra with the P18BF fault code?

Continuing to drive with the Internal Mode Switch 'A' Circuit Stuck On Invalid Voltage Range can lead to further transmission problems and potential safety hazards. It is advisable to address the issue promptly.

6. How much does it cost to repair the P18BF code in a 2018 GMC Sierra?

The cost of repairing the P18BF code can vary depending on the extent of the damage and whether you choose to DIY or seek professional help. Costs may include parts, labor, and diagnostic fees.

7. Can resetting the OBDII system clear the P18BF fault code in a 2018 GMC Sierra?

Resetting the OBDII system may temporarily clear the fault code, but if the underlying issue with the internal mode switch or circuit remains unresolved, the code is likely to reappear.

8. How long does it typically take to repair the Internal Mode Switch 'A' Circuit issue in a 2018 GMC Sierra?

The repair time for the P18BF fault code can vary based on the complexity of the diagnosis and the extent of the repair needed. It may take a few hours to a day for a professional technician to address the issue.

9. Are there any preventive measures to avoid the recurrence of the P18BF code in my 2018 GMC Sierra?

Regular vehicle maintenance, including checking the transmission system, wiring, and internal mode switch, can help prevent the reoccurrence of the P18BF fault code in your GMC Sierra.

10. Can a faulty battery or alternator cause the P18BF fault code in a 2018 GMC Sierra?

While a faulty battery or alternator can potentially affect the electrical system of the vehicle, they are not typically direct causes of the Internal Mode Switch 'A' Circuit Stuck On Invalid Voltage Range code.