AutoCodes – GMC – P18BC 2016 GMC Sierra

P18BC 2016 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 2016 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 2016 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 2016 GMC Sierra - Internal Mode Switch 'C' Circuit Stuck Off Invalid Voltage Range - AutoCodes.com — P18BC 2016 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 2016 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 2016 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 2016 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 2016 GMC Sierra code?

Need more information on how to fix the P18BC 2016 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 2016 GMC Sierra Code

1. What are the common symptoms of OBDII code P18BC on a 2016 GMC Sierra?

- Common symptoms include issues with shifting gears, problems with starting the vehicle, and the inability to switch between different driving modes.

2. What does the Internal Mode Switch 'C' Circuit Stuck Off Invalid Voltage Range mean in relation to the P18BC code?

- This indicates that there is an issue with the internal mode switch circuit 'C' in the vehicle, specifically related to an invalid voltage range being detected.

3. What are the possible causes of the Internal Mode Switch 'C' Circuit Stuck Off Invalid Voltage Range code?

- Possible causes 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 cause of the P18BC code on my 2016 GMC Sierra?

- Diagnosing the issue may involve using a diagnostic scanner to retrieve the trouble codes, inspecting the internal mode switch and its wiring, and testing the voltage in the circuit.

5. Can I continue driving my GMC Sierra with the P18BC code present?

- It is not recommended to continue driving the vehicle with this code present, as it can lead to further damage to the transmission and affect the overall drivability of the vehicle.

6. How can I repair the Internal Mode Switch 'C' Circuit Stuck Off Invalid Voltage Range issue on my GMC Sierra?

- Repairing the issue 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 the P18BC code on a 2016 GMC Sierra without fixing the underlying issue?

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

8. Are there any DIY tips for addressing the P18BC code on a 2016 GMC Sierra?

- DIY tips may include checking for loose or damaged wiring, ensuring proper connections to the internal mode switch, and consulting the vehicle's service manual for specific repair procedures.

9. How long does it typically take to repair the Internal Mode Switch 'C' Circuit Stuck Off Invalid Voltage Range issue?

- The repair time can vary depending on the exact cause of the issue, but it may take a few hours to a full day to diagnose and fix the problem effectively.

10. Will fixing the Internal Mode Switch 'C' Circuit issue solve other transmission-related problems in my 2016 GMC Sierra?

- Fixing the internal mode switch circuit issue may help resolve certain transmission-related issues, but it's essential to address any additional trouble codes and perform thorough testing to ensure proper functionality.