AutoCodes – GMC – P18BB GMC

P18BB GMC 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 GMC 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 1,000

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

What does this mean?

What are the Possible Causes of the DTC P18BB GMC?

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 GMC?

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 GMC 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 GMC code?

Need more information on how to fix the P18BB GMC code? Get Access to Factory Service Manuals

Need Help with the Code?

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Information for Specific GMC Models

P18BB 2014 GMC Sierra — Internal Mode Switch 'B' Circuit Stuck Off Invalid Voltage Range
P18BB 2015 GMC Sierra — Internal Mode Switch 'B' Circuit Stuck Off Invalid Voltage Range
P18BB 2016 GMC Sierra — Internal Mode Switch 'B' Circuit Stuck Off Invalid Voltage Range
P18BB 2017 GMC Sierra — Internal Mode Switch 'B' Circuit Stuck Off Invalid Voltage Range
P18BB 2018 GMC Sierra — Internal Mode Switch 'B' Circuit Stuck Off Invalid Voltage Range

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 GMC Code

1. What are the common symptoms of OBDII code P18BB GMC?

- Common symptoms include issues with shifting gears, the transmission staying in one gear, difficulty starting the vehicle, and the check engine light being illuminated.

2. What can cause the Internal Mode Switch 'B' Circuit Stuck Off Invalid Voltage Range code to appear?

- Possible causes include a faulty internal mode switch, damaged wiring or connectors in the circuit, low battery voltage, or issues with the transmission control module.

3. How serious is the P18BB GMC code?

- This code can affect the proper functioning of your vehicle's transmission system, leading to potential driving issues. It is recommended to address the problem promptly to prevent further damage.

4. How can I diagnose the Internal Mode Switch 'B' Circuit Stuck Off issue?

- Diagnosing this code may involve using a scan tool to check for related trouble codes, testing the internal mode switch, inspecting the wiring and connectors, and checking battery voltage levels.

5. Can I drive my vehicle with the P18BB code present?

- It is not recommended to drive your vehicle with this code present, as it can lead to transmission problems and potential safety hazards. It's best to have the issue resolved before driving.

6. How can I repair the Internal Mode Switch 'B' Circuit Stuck Off Invalid Voltage Range code?

- Repair options may include replacing the internal mode switch, repairing or replacing damaged wiring/connectors, addressing battery voltage issues, or reprogramming the transmission control module.

7. Will resetting the trouble codes make the P18BB GMC code disappear?

- Resetting the trouble codes may temporarily clear the check engine light, but if the underlying issue causing the P18BB code is not fixed, the code is likely to reappear after driving the vehicle.

8. Is it possible to prevent the Internal Mode Switch 'B' Circuit Stuck Off code from occurring?

- Regular maintenance checks, prompt addressing of transmission issues, and ensuring proper battery voltage levels can help prevent the occurrence of this OBDII trouble code.

9. Can a DIY enthusiast fix the P18BB GMC code at home?

- Depending on your automotive repair skills and access to tools, you may be able to diagnose and address the P18BB code at home. However, for complex issues, it is recommended to consult a professional mechanic.

10. How much does it cost to repair the Internal Mode Switch 'B' Circuit Stuck Off Invalid Voltage Range code?

- The cost of repairing this code can vary depending on the underlying issue, parts needed, labor costs, and your location. It is advisable to obtain quotes from auto repair shops for an accurate estimate.