AutoCodes – GMC – P18C0 2018 GMC Sierra

P18C0 2018 GMC Sierra Code - Internal Mode Switch 'B' Circuit Stuck On Invalid Voltage Range

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: P18C0 2018 GMC Sierra indicates Internal Mode Switch 'B' Circuit Stuck On Invalid Voltage Range.
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 406

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 P18C0 2018 GMC Sierra 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 has an invalid voltage range of 0.70 – 0.96 V for 2.7 s.

OBDII Code P18C0 2018 GMC Sierra - Internal Mode Switch 'B' Circuit Stuck On Invalid Voltage Range - AutoCodes.com — P18C0 2018 GMC Sierra Code - Internal Mode Switch 'B' Circuit Stuck On Invalid Voltage Range

What does this mean?

What are the Possible Causes of the DTC P18C0 2018 GMC Sierra?

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 P18C0 2018 GMC Sierra?

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 P18C0 2018 GMC Sierra 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 P18C0 2018 GMC Sierra code?

Need more information on how to fix the P18C0 2018 GMC Sierra code? Get Access to Factory Service Manuals

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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 P18C0 2018 GMC Sierra Code

1. What are the common symptoms of OBDII code P18C0 in a 2018 GMC Sierra?

The common symptoms of code P18C0 include issues with shifting gears, the inability to start the vehicle, and the transmission getting stuck in one gear.

2. What does the OBDII code P18C0 'Internal Mode Switch 'B' Circuit Stuck On Invalid Voltage Range' mean for a 2018 GMC Sierra?

This code indicates that there is a problem with the internal mode switch 'B' circuit in the transmission of the 2018 GMC Sierra, specifically related to an invalid voltage range.

3. What are the potential causes of OBDII code P18C0 in a 2018 GMC Sierra?

Possible causes of code P18C0 include a faulty internal mode switch, damaged wiring or connectors in the circuit, low transmission fluid levels, or issues with the transmission control module.

4. How can I diagnose OBDII code P18C0 in my 2018 GMC Sierra?

Diagnosing code P18C0 involves using a scan tool to retrieve the code, checking the internal mode switch and related circuitry for any visible damage, and testing the voltage range to pinpoint the issue accurately.

5. Can I continue to drive my 2018 GMC Sierra with OBDII code P18C0?

It is not recommended to drive your vehicle with code P18C0 active as it can lead to transmission problems and potential safety hazards. It's best to address the issue promptly.

6. What are some repair tips for fixing OBDII code P18C0 in a 2018 GMC Sierra?

Repair tips for resolving code P18C0 include inspecting and replacing the internal mode switch, repairing any damaged wiring or connectors, ensuring proper transmission fluid levels, and resetting the code after repairs.

7. How much does it typically cost to repair OBDII code P18C0 in a 2018 GMC Sierra?

The cost of repairing code P18C0 can vary depending on the exact cause of the issue, the parts needed for replacement, and labor costs. It's advisable to consult a professional mechanic for an accurate estimate.

8. Can I reset OBDII code P18C0 in my 2018 GMC Sierra using a simple OBDII scanner?

Resetting code P18C0 may be possible with an OBDII scanner by clearing the code after addressing the underlying issue. However, it's crucial to fix the root cause first to prevent the code from reappearing.

9. Is OBDII code P18C0 in a 2018 GMC Sierra a serious problem?

Code P18C0 can potentially lead to significant transmission issues if left unresolved, so it's essential to address the problem promptly to avoid further damage and ensure the vehicle's safe operation.

10. How long does it take to repair OBDII code P18C0 in a 2018 GMC Sierra?

The time required to repair code P18C0 can vary based on the specific cause of the issue, the availability of parts, and the mechanic's expertise. Some repairs may be completed within a few hours, while more complex issues may take longer.