AutoCodes – GMC – P18BC 2018 GMC Sierra

P18BC 2018 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 2018 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.

Save to My Repairs My Repairs

AI answers can be wrong. Verify repairs with testing. Open full chat

Code Popularity 185

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
Add Comment

💬 Need more help? Ask Coddy for instant answers — it's free!

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

OBDII Code P18BC 2018 GMC Sierra - Internal Mode Switch 'C' Circuit Stuck Off Invalid Voltage Range - AutoCodes.com — P18BC 2018 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 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 P18BC 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 P18BC 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 P18BC 2018 GMC Sierra code?

Need more information on how to fix the P18BC 2018 GMC Sierra code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P18BC 2018 GMC Sierra code diagnosed by a professional: Find a repair shop in your area

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 2018 GMC Sierra Code

1. What are the common symptoms of OBDII code P18BC on a 2018 GMC Sierra?

The common symptoms of OBDII code P18BC on a 2018 GMC Sierra include issues with shifting gears, the transmission not engaging properly, and possible illumination of the Check Engine Light.

2. What does the OBDII code P18BC for a 2018 GMC Sierra mean?

OBDII code P18BC for a 2018 GMC Sierra refers to the Internal Mode Switch 'C' Circuit Stuck Off Invalid Voltage Range, indicating a problem with the transmission range sensor.

3. What are the possible causes of OBDII code P18BC on a 2018 GMC Sierra?

Possible causes of OBDII code P18BC on a 2018 GMC Sierra include a faulty transmission range sensor, damaged wiring or connectors, or internal transmission issues.

4. How serious is OBDII code P18BC on a 2018 GMC Sierra?

OBDII code P18BC on a 2018 GMC Sierra should be addressed promptly as it can lead to transmission-related issues, affecting the vehicle's drivability and potentially causing further damage if left unresolved.

5. Can OBDII code P18BC on a 2018 GMC Sierra be fixed at home?

Depending on the underlying cause, fixing OBDII code P18BC on a 2018 GMC Sierra may be possible at home if you have the necessary tools, knowledge, and skills. However, some cases may require professional diagnosis and repair.

6. How can I diagnose OBDII code P18BC on my 2018 GMC Sierra?

Diagnosing OBDII code P18BC on a 2018 GMC Sierra involves using an OBDII scanner to retrieve the code, checking the transmission range sensor, inspecting wiring and connectors for damage, and performing a thorough transmission system evaluation.

7. What are some repair tips for fixing OBDII code P18BC on a 2018 GMC Sierra?

Repair tips for fixing OBDII code P18BC on a 2018 GMC Sierra include checking and repairing any damaged wiring or connectors, replacing the transmission range sensor if faulty, and ensuring proper reassembly of components during repair.

8. Is it safe to continue driving with OBDII code P18BC on a 2018 GMC Sierra?

It is not recommended to continue driving with OBDII code P18BC on a 2018 GMC Sierra, as it can lead to transmission issues and potential safety hazards. It is best to address the problem promptly.

9. How much does it cost to repair OBDII code P18BC on a 2018 GMC Sierra?

The cost to repair OBDII code P18BC on a 2018 GMC Sierra can vary depending on the underlying cause, location, and labor rates. It is advisable to obtain quotes from different repair shops for an accurate estimate.

10. Can resetting the OBDII code P18BC on a 2018 GMC Sierra fix the issue?

Simply resetting the OBDII code P18BC on a 2018 GMC Sierra may temporarily clear the Check Engine Light, but it will not fix the underlying problem causing the code. Proper diagnosis and repair are necessary to address the issue effectively.