AutoCodes – GMC – P18B7 GMC

P18B7 GMC Code - Internal Mode Switch 'C' 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: P18B7 GMC indicates Internal Mode Switch 'C' 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 1,702

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 P18B7 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 C signal circuit voltage is between 0.966–1.68 V, for 1.75 s.

OBDII Code P18B7 GMC - Internal Mode Switch 'C' Circuit Shorted - AutoCodes.com — P18B7 GMC Code - Internal Mode Switch 'C' Circuit Shorted

What does this mean?

What are the Possible Causes of the DTC P18B7 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 P18B7 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 P18B7 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 P18B7 GMC code?

Need more information on how to fix the P18B7 GMC code? Get Access to Factory Service Manuals

Need Help with the Code?

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Information for Specific GMC Models

P18B7 2014 GMC Sierra — Internal Mode Switch 'C' Circuit Shorted
P18B7 2015 GMC Sierra — Internal Mode Switch 'C' Circuit Shorted
P18B7 2016 GMC Sierra — Internal Mode Switch 'C' Circuit Shorted
P18B7 2017 GMC Sierra — Internal Mode Switch 'C' Circuit Shorted
P18B7 2018 GMC Sierra — Internal Mode Switch 'C' 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 P18B7 GMC Code

1. What are the common symptoms of OBDII code P18B7 GMC?

The common symptoms of code P18B7 GMC include erratic shifting behavior, the inability to shift gears, and illumination of the Check Engine Light.

2. What does the OBDII code P18B7 GMC mean?

The code P18B7 GMC indicates a malfunction in the Internal Mode Switch 'C' circuit, specifically a short circuit.

3. What are the possible causes of OBDII code P18B7 GMC?

Possible causes of code P18B7 GMC include a faulty internal mode switch, damaged wiring in the circuit, or a poor connection in the switch circuit.

4. How do you diagnose OBDII code P18B7 GMC?

Diagnosing code P18B7 GMC involves inspecting the internal mode switch, checking for damaged wiring, and testing the circuit for proper voltage and continuity.

5. Can I continue driving with OBDII code P18B7 GMC?

It is not recommended to drive with code P18B7 GMC present, as it can lead to further transmission issues and potential safety hazards.

6. How do I repair OBDII code P18B7 GMC?

To repair code P18B7 GMC, you may need to replace the internal mode switch, repair any damaged wiring, or address any poor connections in the circuit.

7. Will resetting the trouble codes make OBDII code P18B7 GMC go away?

Resetting the trouble codes may temporarily clear the Check Engine Light, but if the underlying issue causing code P18B7 GMC is not addressed, the code is likely to reappear.

8. Can a DIY enthusiast fix OBDII code P18B7 GMC?

Depending on your skill level and access to tools, a DIY enthusiast may be able to diagnose and repair code P18B7 GMC by following a service manual or online guides.

9. How much does it cost to fix OBDII code P18B7 GMC at a repair shop?

The cost of fixing code P18B7 GMC at a repair shop can vary depending on the specific issue, but it may involve a diagnostic fee, parts replacement, and labor costs.

10. How urgent is it to address OBDII code P18B7 GMC?

It is important to address code P18B7 GMC promptly to prevent further damage to the transmission system and ensure the vehicle operates safely and efficiently.