AutoCodes – GMC – P18B5 GMC

P18B5 GMC Code - Internal Mode Switch 'A' 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: P18B5 GMC indicates Internal Mode Switch 'A' 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 1,729

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 P18B5 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 A signal circuit voltage is between 0.966–1.68 V, for 1.75 s.

OBDII Code P18B5 GMC - Internal Mode Switch 'A' Circuit Shorted - AutoCodes.com — P18B5 GMC Code - Internal Mode Switch 'A' Circuit Shorted

What does this mean?

What are the Possible Causes of the DTC P18B5 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 P18B5 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 P18B5 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 P18B5 GMC code?

Need more information on how to fix the P18B5 GMC code? Get Access to Factory Service Manuals

Need Help with the Code?

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Information for Specific GMC Models

P18B5 2014 GMC Sierra — Internal Mode Switch 'A' Circuit Shorted
P18B5 2015 GMC Sierra — Internal Mode Switch 'A' Circuit Shorted
P18B5 2016 GMC Sierra — Internal Mode Switch 'A' Circuit Shorted
P18B5 2017 GMC Sierra — Internal Mode Switch 'A' Circuit Shorted
P18B5 2018 GMC Sierra — Internal Mode Switch 'A' 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 P18B5 GMC Code

1. What are the common symptoms of OBDII code P18B5 GMC?

The common symptoms of code P18B5 GMC include issues with shifting gears, hesitation when accelerating, and problems with the vehicle entering or staying in certain gears.

2. What are the possible causes of the Internal Mode Switch 'A' Circuit Shorted code?

The code P18B5 GMC typically indicates a short circuit in the internal mode switch circuit. This can be caused by damaged wiring, a faulty internal mode switch, or a problem with the transmission control module.

3. How serious is the P18B5 GMC fault code?

The P18B5 GMC fault code can affect the performance and drivability of your vehicle. It is recommended to address this issue promptly to prevent further transmission-related problems.

4. Can I still drive my vehicle with the Internal Mode Switch 'A' Circuit Shorted code?

It is not recommended to drive your vehicle with the P18B5 GMC code present, as it can lead to transmission issues and potentially cause further damage. It is best to have the issue diagnosed and repaired as soon as possible.

5. How can I diagnose the Internal Mode Switch 'A' Circuit Shorted code?

Diagnosing the P18B5 GMC code typically involves using a scan tool to retrieve the fault codes stored in the vehicle's computer system. Further testing may be required to pinpoint the exact cause of the issue.

6. Is it possible to repair the Internal Mode Switch 'A' Circuit Shorted code myself?

Repairing the P18B5 GMC code may require advanced diagnostic equipment and knowledge of automotive electrical systems. It is recommended to have a qualified mechanic or technician address this issue.

7. What are some tips for repairing the P18B5 GMC fault code?

Some tips for repairing the P18B5 GMC code include inspecting the wiring harness for damage, testing the internal mode switch for proper operation, and checking the transmission control module for faults.

8. Can a faulty internal mode switch cause the P18B5 GMC fault code?

Yes, a faulty internal mode switch can cause the P18B5 GMC fault code to be triggered. It is one of the potential causes of a short circuit in the internal mode switch circuit.

9. How much does it cost to repair the Internal Mode Switch 'A' Circuit Shorted code?

The cost of repairing the P18B5 GMC fault code can vary depending on the exact cause of the issue, the labor rates in your area, and the cost of parts needed for the repair. It is best to get a professional diagnosis for an accurate estimate.

10. Can resetting the fault codes clear the P18B5 GMC code?

Resetting the fault codes may temporarily clear the P18B5 GMC code, but if the underlying issue is not addressed, the code is likely to return. It is important to diagnose and repair the root cause of the problem to prevent future issues.