AutoCodes – GMC – P18B6 GMC

P18B6 GMC Code - Internal Mode Switch 'B' Circuit Shorted

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: P18B6 GMC indicates Internal Mode Switch 'B' Circuit Shorted.
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 1,177

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 P18B6 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 voltage is between 0.966–1.68 V, for 1.75 s.

OBDII Code P18B6 GMC - Internal Mode Switch 'B' Circuit Shorted - AutoCodes.com — P18B6 GMC Code - Internal Mode Switch 'B' Circuit Shorted

What does this mean?

What are the Possible Causes of the DTC P18B6 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 P18B6 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 P18B6 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 P18B6 GMC code?

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Need Help with the Code?

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Information for Specific GMC Models

P18B6 2014 GMC Sierra — Internal Mode Switch 'B' Circuit Shorted
P18B6 2015 GMC Sierra — Internal Mode Switch 'B' Circuit Shorted
P18B6 2016 GMC Sierra — Internal Mode Switch 'B' Circuit Shorted
P18B6 2017 GMC Sierra — Internal Mode Switch 'B' Circuit Shorted
P18B6 2018 GMC Sierra — Internal Mode Switch 'B' Circuit Shorted

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 P18B6 GMC Code

1. What are common symptoms of the OBDII code P18B6 GMC?

- Common symptoms include issues with shifting gears, difficulty starting the vehicle, and the transmission not engaging properly.

2. What causes the Internal Mode Switch 'B' Circuit Shorted error code?

- The P18B6 code is typically triggered by a short circuit in the internal mode switch 'B' circuit, which is responsible for detecting the gear position.

3. How can I diagnose the Internal Mode Switch 'B' Circuit Shorted issue?

- Diagnosing this issue involves checking the wiring and connectors related to the internal mode switch, as well as testing the switch itself for proper functionality.

4. Can a faulty internal mode switch cause the P18B6 code?

- Yes, a faulty internal mode switch can cause the P18B6 code to be triggered, especially if there is a short circuit in the 'B' circuit.

5. Is it safe to continue driving with the P18B6 error code present?

- It is not recommended to drive with the P18B6 code present, as it can lead to further transmission problems and potentially unsafe driving conditions.

6. How can I repair the Internal Mode Switch 'B' Circuit Shorted issue?

- Repairing this issue involves replacing the internal mode switch if it is faulty, repairing any damaged wiring, and clearing the error code using an OBDII scanner.

7. Can I reset the P18B6 code myself, or do I need a professional to do it?

- You can attempt to clear the P18B6 code yourself using an OBDII scanner, but it is recommended to address the underlying issue causing the code to prevent it from reoccurring.

8. Will the P18B6 code cause my vehicle to fail an emissions test?

- Yes, the P18B6 code can cause your vehicle to fail an emissions test, as it indicates a problem with the transmission system that can affect emissions.

9. How much does it typically cost to repair the Internal Mode Switch 'B' Circuit Shorted issue?

- The cost of repairing the P18B6 code can vary depending on the extent of the damage and whether you choose to do the repairs yourself or have them done by a professional mechanic.

10. Can a DIY enthusiast with basic mechanical skills fix the Internal Mode Switch 'B' Circuit Shorted problem?

- Depending on your level of expertise, a DIY enthusiast with basic mechanical skills may be able to diagnose and repair the internal mode switch 'B' circuit shorted issue, but it is recommended to proceed with caution and seek professional help if needed.