AutoCodes – GMC – P18BB 2018 GMC Sierra

P18BB 2018 GMC Sierra Code - Internal Mode Switch 'B' 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: P18BB 2018 GMC Sierra indicates Internal Mode Switch 'B' 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 163

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 P18BB 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 B signal circuit has an invalid voltage range of 1.68 – 2.38 V for 2.7 s.

OBDII Code P18BB 2018 GMC Sierra - Internal Mode Switch 'B' Circuit Stuck Off Invalid Voltage Range - AutoCodes.com — P18BB 2018 GMC Sierra Code - Internal Mode Switch 'B' Circuit Stuck Off Invalid Voltage Range

What does this mean?

What are the Possible Causes of the DTC P18BB 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 P18BB 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 P18BB 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 P18BB 2018 GMC Sierra code?

Need more information on how to fix the P18BB 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 P18BB 2018 GMC Sierra Code

1. What are the common symptoms of OBDII code P18BB on a 2018 GMC Sierra?

The common symptoms include issues with shifting gears, rough shifting, hesitation during acceleration, and in some cases, the vehicle may not start.

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

This code indicates a problem with the internal mode switch in the transmission control module, specifically related to an invalid voltage range being detected.

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

Possible causes include a faulty internal mode switch, damaged wiring or connectors, a malfunctioning transmission control module, or low voltage in the system.

4. How can I diagnose the cause of OBDII code P18BB on my 2018 GMC Sierra?

Diagnosis typically involves checking the internal mode switch for proper operation, inspecting the wiring and connectors for damage, testing the voltage levels, and scanning the transmission control module for any related faults.

5. Can I continue driving my GMC Sierra with the Internal Mode Switch 'B' Circuit Stuck Off Invalid Voltage Range code?

It is not recommended to drive the vehicle with this code present, as it can lead to further transmission issues and potential safety hazards. It is best to address the problem promptly.

6. What are some repair tips for fixing OBDII code P18BB on a 2018 GMC Sierra?

Repair tips may include replacing the internal mode switch if it is faulty, repairing any damaged wiring or connectors, resetting the transmission control module, and ensuring the system has proper voltage levels.

7. Is it possible to reset the OBDII code P18BB on my GMC Sierra without fixing the underlying issue?

While you can clear the code using an OBDII scanner, it is important to address the root cause of the problem to prevent further issues and ensure the proper functioning of your vehicle.

8. How much does it typically cost to repair OBDII code P18BB on a 2018 GMC Sierra?

The cost of repairs can vary depending on the exact cause of the issue, but it may involve parts replacement, labor costs, and diagnostic fees. It is advisable to consult a professional mechanic for an accurate estimate.

9. Can a DIY enthusiast fix the Internal Mode Switch 'B' Circuit Stuck Off Invalid Voltage Range code on a GMC Sierra?

While some basic troubleshooting and repairs may be possible for experienced DIY enthusiasts, diagnosing and fixing complex transmission-related issues like this code often require specialized tools and expertise best left to professional mechanics.

10. How long does it typically take to repair OBDII code P18BB on a 2018 GMC Sierra?

The repair time can vary based on the specific cause of the issue, the availability of parts, and the mechanic's workload. It is advisable to consult with a professional technician for an estimated repair timeline.