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P18B6 2015 GMC Sierra Code - Internal Mode Switch 'B' Circuit Shorted

Quick Answer

The P18B6 diagnostic trouble code for a 2015 GMC Sierra indicates that there is a short circuit in the internal mode switch 'B' circuit. Common causes include Damaged internal mode switch, Short circuit in the internal mode switch circuit, Corrosion or loose connections in the wiring harness. 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 2015 GMC Sierra indicates Internal Mode Switch 'B' Circuit Shorted.
Common causes
Common causes include Damaged internal mode switch, Short circuit in the internal mode switch circuit, Corrosion or loose connections in the wiring harness.
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.
What is this?
Table of contents Created and updated by William Orellana on Sep 11, 2024
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Code P18B6 2015 GMC Sierra Description

The P18B6 diagnostic trouble code for a 2015 GMC Sierra indicates that there is a short circuit in the internal mode switch 'B' circuit. The internal mode switch, also known as the IMS, is a crucial component in the transmission system that helps control the gear selection and shifting process. When the internal mode switch 'B' circuit is shorted, it can lead to issues with the transmission shifting correctly, causing erratic behavior and potentially affecting the vehicle's overall performance.

OBDII Code P18B6 2015 GMC Sierra - Internal Mode Switch 'B' Circuit Shorted
P18B6 2015 GMC Sierra Code - Internal Mode Switch 'B' Circuit Shorted

Common Causes of P18B6 2015 GMC Sierra

  1. Damaged internal mode switch
  2. Short circuit in the internal mode switch circuit
  3. Corrosion or loose connections in the wiring harness
  4. Faulty transmission control module (TCM)
  5. Electrical issues within the transmission system

Symptoms of P18B6 2015 GMC Sierra

  1. Erratic shifting behavior
  2. Transmission getting stuck in a particular gear
  3. Harsh shifting
  4. Delayed gear engagement
  5. Illumination of the check engine light

How to Fix P18B6 2015 GMC Sierra

  1. Diagnose the internal mode switch 'B' circuit using a scan tool to confirm the specific issue.
  2. Inspect the internal mode switch and wiring harness for any signs of damage, corrosion, or loose connections.
  3. Replace the internal mode switch if it is found to be faulty.
  4. Repair any damaged wiring or connectors in the internal mode switch circuit.
  5. Clear the trouble codes and test drive the vehicle to ensure the issue has been resolved.

Cost to Fix P18B6 2015 GMC Sierra

The typical repair cost for addressing the internal mode switch 'B' circuit shorted code can range from $200 to $500, including parts and labor. However, it is essential to note that the actual cost can vary based on factors such as the location of the repair shop, the specific make and model of the vehicle, and the extent of the damage. Additionally, diagnosis time and labor rates at auto repair shops can vary, with hourly rates typically ranging between $80 and $150. It is advisable to consult with local repair shops to get a more accurate estimate for this repair.

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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 P18B6 2015 GMC Sierra Code

1. What are the common symptoms of OBDII code P18B6 in a 2015 GMC Sierra?

The common symptoms of code P18B6 include issues with shifting gears, the transmission not engaging properly, and the check engine light illuminating on the dashboard.

2. What does the OBDII code P18B6 'Internal Mode Switch B Circuit Shorted' mean for a 2015 GMC Sierra?

The code P18B6 indicates a problem with the internal mode switch 'B' circuit, specifically a short circuit. This affects the proper communication between the transmission control module and the internal mode switch.

3. What are the possible causes of OBDII code P18B6 in a 2015 GMC Sierra?

Common causes of code P18B6 include a faulty internal mode switch, damaged wiring or connectors in the circuit, a short circuit in the internal mode switch 'B' circuit, or issues with the transmission control module.

4. How can I diagnose OBDII code P18B6 in a 2015 GMC Sierra?

Diagnosing code P18B6 involves using a scan tool to retrieve the code, inspecting the internal mode switch 'B' circuit for any visible damage, checking the wiring and connectors, and conducting a thorough inspection of the transmission control module.

5. Is it safe to continue driving a 2015 GMC Sierra with OBDII code P18B6 present?

It is not recommended to continue driving the vehicle with code P18B6 present, as it can lead to transmission issues and potential safety hazards. It's best to address the problem promptly to avoid further damage.

6. Can I repair OBDII code P18B6 in a 2015 GMC Sierra myself?

While some DIY enthusiasts may attempt to repair code P18B6 themselves by replacing the internal mode switch, it's recommended to consult a professional mechanic for an accurate diagnosis and proper repair to ensure the issue is resolved correctly.

7. How much does it typically cost to fix OBDII code P18B6 in a 2015 GMC Sierra?

The cost of repairing code P18B6 can vary depending on the root cause of the issue, the extent of the damage, and labor costs. It's advisable to get multiple quotes from reputable auto repair shops to compare prices.

8. Will resetting the OBDII code P18B6 in a 2015 GMC Sierra make it go away permanently?

Simply resetting the code may temporarily turn off the check engine light, but it will not fix the underlying issue causing code P18B6. It's crucial to diagnose and repair the problem to prevent it from reoccurring.

9. Can a low battery voltage trigger OBDII code P18B6 in a 2015 GMC Sierra?

Low battery voltage can potentially cause electrical issues that may lead to code P18B6 being triggered. Ensuring the battery is in good condition and properly charged is essential in maintaining the vehicle's electrical system.

10. How long does it typically take to repair OBDII code P18B6 in a 2015 GMC Sierra?

The repair time for code P18B6 can vary depending on the exact cause of the issue, the availability of parts, and the mechanic's expertise. In some cases, it can be resolved within a few hours, while more complex repairs may take longer.

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