AutoCodes – GMC – P18BC 2017 GMC Sierra

P18BC 2017 GMC Sierra Code - Internal Mode Switch 'C' Circuit Stuck Off 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: P18BC 2017 GMC Sierra indicates Internal Mode Switch 'C' Circuit Stuck Off 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 174

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 P18BC 2017 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 C signal circuit has an invalid voltage range of 1.68 – 2.38 V, for 2.7 s.

OBDII Code P18BC 2017 GMC Sierra - Internal Mode Switch 'C' Circuit Stuck Off Invalid Voltage Range - AutoCodes.com — P18BC 2017 GMC Sierra Code - Internal Mode Switch 'C' Circuit Stuck Off Invalid Voltage Range

What does this mean?

What are the Possible Causes of the DTC P18BC 2017 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 P18BC 2017 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 P18BC 2017 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 P18BC 2017 GMC Sierra code?

Need more information on how to fix the P18BC 2017 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 P18BC 2017 GMC Sierra Code

1. What are the common symptoms of OBDII code P18BC in a 2017 GMC Sierra?

The common symptoms of OBDII code P18BC in a 2017 GMC Sierra include issues with shifting gears, erratic or harsh shifting, and the inability to shift gears properly.

2. What does the OBDII code P18BC 'Internal Mode Switch 'C' Circuit Stuck Off Invalid Voltage Range' mean for a 2017 GMC Sierra?

The code P18BC indicates that there is an issue with the Internal Mode Switch 'C' circuit in your 2017 GMC Sierra, specifically related to an invalid voltage range.

3. What are the possible causes of OBDII code P18BC in a 2017 GMC Sierra?

Possible causes of OBDII code P18BC in a 2017 GMC Sierra include a faulty internal mode switch, damaged wiring or connectors, low transmission fluid level, or issues with the transmission control module.

4. How can I diagnose the OBDII code P18BC in my 2017 GMC Sierra?

Diagnosing OBDII code P18BC in a 2017 GMC Sierra involves using a scan tool to retrieve the code, checking the internal mode switch and related wiring for faults, inspecting the transmission fluid level, and testing the transmission control module.

5. What are the repair options for OBDII code P18BC in a 2017 GMC Sierra?

Repair options for OBDII code P18BC in a 2017 GMC Sierra may include replacing the internal mode switch, repairing or replacing damaged wiring or connectors, topping up the transmission fluid, or reprogramming the transmission control module.

6. Can I drive my 2017 GMC Sierra with OBDII code P18BC?

It is not recommended to drive your 2017 GMC Sierra with OBDII code P18BC, as it can lead to further transmission issues and potential safety hazards. It's best to address the problem promptly.

7. How serious is OBDII code P18BC in a 2017 GMC Sierra?

OBDII code P18BC in a 2017 GMC Sierra should be taken seriously, as it can affect the proper functioning of the transmission system, leading to potential drivability issues and safety concerns.

8. How much does it cost to repair OBDII code P18BC in a 2017 GMC Sierra?

The cost to repair OBDII code P18BC in a 2017 GMC Sierra can vary depending on the specific cause of the issue, parts needed for repair, and labor costs. It's recommended to consult a mechanic for an accurate estimate.

9. Can a DIY enthusiast fix OBDII code P18BC in a 2017 GMC Sierra?

Depending on your skill level and access to tools, a DIY enthusiast may be able to address OBDII code P18BC in a 2017 GMC Sierra by performing basic diagnostic steps or simpler repairs like checking wiring connections. However, more complex issues may require professional assistance.

10. How can I prevent OBDII code P18BC from occurring in my 2017 GMC Sierra?

To prevent OBDII code P18BC in your 2017 GMC Sierra, it's important to regularly maintain your vehicle, including checking transmission fluid levels, addressing any warning signs promptly, and following the manufacturer's recommended service schedule.