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P18B6 2018 GMC Sierra Code - Internal Mode Switch 'B' Circuit Shorted

Quick Answer

The P18B6 diagnostic trouble code (DTC) indicates an issue with the Internal Mode Switch 'B' Circuit in a 2018 GMC Sierra. Common causes include Damaged or frayed wiring in the Internal Mode Switch 'B' circuit, Corrosion or poor connections at the switch or wiring harness, A faulty Internal Mode Switch that is unable to send proper signals to the PCM. 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 2018 GMC Sierra indicates Internal Mode Switch 'B' Circuit Shorted.
Common causes
Common causes include Damaged or frayed wiring in the Internal Mode Switch 'B' circuit, Corrosion or poor connections at the switch or wiring harness, A faulty Internal Mode Switch that is unable to send proper signals to the PCM.
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 Oct 08, 2024
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Code P18B6 2018 GMC Sierra Description

The P18B6 diagnostic trouble code (DTC) indicates an issue with the Internal Mode Switch 'B' Circuit in a 2018 GMC Sierra. This code is triggered when the vehicle's powertrain control module (PCM) detects a short circuit in the wiring or components associated with the Internal Mode Switch 'B'. The Internal Mode Switch is part of the transmission control system, which plays a crucial role in determining the operational mode of the transmission, such as Park, Reverse, Neutral, and Drive.

OBDII Code P18B6 2018 GMC Sierra - Internal Mode Switch 'B' Circuit Shorted
P18B6 2018 GMC Sierra Code - Internal Mode Switch 'B' Circuit Shorted

Common Causes of P18B6 2018 GMC Sierra

  1. Damaged or frayed wiring in the Internal Mode Switch 'B' circuit.
  2. Corrosion or poor connections at the switch or wiring harness.
  3. A faulty Internal Mode Switch that is unable to send proper signals to the PCM.
  4. A malfunctioning PCM that misinterprets the signals from the Internal Mode Switch.
  5. Environmental factors, such as moisture intrusion, leading to electrical shorts.

Symptoms of P18B6 2018 GMC Sierra

  1. Erratic or harsh shifting of the transmission.
  2. Inability to shift into certain gears or getting stuck in one gear.
  3. Activation of the check engine light.
  4. Reduced fuel efficiency due to improper transmission operation.
  5. Engaging limp mode, where the vehicle limits its speed and power.

How to Fix P18B6 2018 GMC Sierra

  1. Visual Inspection: Start with a thorough visual inspection of the wiring and connectors associated with the Internal Mode Switch 'B' circuit for any signs of damage, corrosion, or loose connections.
  2. Test the Switch: Use a multimeter to test the Internal Mode Switch for proper operation. If the switch is faulty, it will need to be replaced.
  3. Repair Wiring: If damaged wiring is found, repair or replace the affected sections of the wiring harness to ensure proper electrical connectivity.
  4. Clear Codes and Test Drive: After repairs, clear the diagnostic trouble codes using a scan tool and perform a test drive to ensure the issue has been resolved and the code does not return.
  5. Recheck Connections: After the test drive, recheck all connections and wiring to ensure everything is secure and functioning correctly.

Cost to Fix P18B6 2018 GMC Sierra

The cost to repair the P18B6 code can vary significantly based on the specific issue identified during diagnosis. On average, repair costs can range from $150 to $600. This estimate includes parts such as a new Internal Mode Switch (if needed) and labor costs. Labor rates typically range from $80 to $150 per hour, depending on the location, vehicle make and model, and engine type. In metropolitan areas or at dealerships, rates may be higher, while independent shops often offer lower rates. It is advisable to check local rates for a more precise estimate and to obtain a detailed quote after a thorough diagnosis.

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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 2018 GMC Sierra Code

1. What does OBDII code P18B6 on a 2018 GMC Sierra mean?

The code P18B6 indicates an issue with the Internal Mode Switch 'B' Circuit Shorted in the vehicle's transmission control module.

2. What are the common symptoms of OBDII code P18B6 in a 2018 GMC Sierra?

Common symptoms of this code may include issues with shifting gears, transmission slipping, or the transmission not responding properly to driver inputs.

3. What are the possible causes of OBDII code P18B6 in a 2018 GMC Sierra?

Possible causes of this code can include a faulty internal mode switch, damaged wiring or connectors in the circuit, or issues with the transmission control module itself.

4. How serious is OBDII code P18B6 in a 2018 GMC Sierra?

Code P18B6 should be addressed promptly as it can lead to drivability issues and potential damage to the transmission if left unresolved.

5. Can I continue driving my 2018 GMC Sierra with OBDII code P18B6?

It is not recommended to continue driving the vehicle with this code present, as it can cause further damage to the transmission system.

6. How can I diagnose OBDII code P18B6 in a 2018 GMC Sierra?

Diagnosis typically involves using a scan tool to retrieve the specific fault codes, inspecting the internal mode switch and related wiring, and testing the transmission control module.

7. How can I repair OBDII code P18B6 in a 2018 GMC Sierra?

Repairing this code may involve replacing the internal mode switch, repairing or replacing damaged wiring, or reprogramming the transmission control module.

8. Can I reset OBDII code P18B6 in a 2018 GMC Sierra with a simple reset tool?

While you can clear the code with an OBDII scanner, it is crucial to address the underlying issue causing the code to prevent it from recurring.

9. How much does it cost to fix OBDII code P18B6 in a 2018 GMC Sierra?

The cost of fixing this code can vary depending on the exact cause of the issue, but it may involve parts replacement and labor costs.

10. Is OBDII code P18B6 a common issue in 2018 GMC Sierra vehicles?

While not extremely common, OBDII code P18B6 can occur in 2018 GMC Sierra vehicles due to various factors affecting the internal mode switch circuit.

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