AutoCodes – GMC – P18C2 GMC

P18C2 GMC Code - Internal Mode Switch 'P' 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: P18C2 GMC indicates Internal Mode Switch 'P' 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 1,439

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 P18C2 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 P signal circuit has an invalid voltage range of 0.70 – 0.96 V for 2.7 s.

OBDII Code P18C2 GMC - Internal Mode Switch 'P' Circuit Stuck On Invalid Voltage Range - AutoCodes.com — P18C2 GMC Code - Internal Mode Switch 'P' Circuit Stuck On Invalid Voltage Range

What does this mean?

What are the Possible Causes of the DTC P18C2 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 P18C2 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 P18C2 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 P18C2 GMC code?

Need more information on how to fix the P18C2 GMC code? Get Access to Factory Service Manuals

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Information for Specific GMC Models

P18C2 2014 GMC Sierra — Internal Mode Switch 'P' Circuit Stuck On Invalid Voltage Range
P18C2 2015 GMC Sierra — Internal Mode Switch 'P' Circuit Stuck On Invalid Voltage Range
P18C2 2016 GMC Sierra — Internal Mode Switch 'P' Circuit Stuck On Invalid Voltage Range
P18C2 2017 GMC Sierra — Internal Mode Switch 'P' Circuit Stuck On Invalid Voltage Range
P18C2 2018 GMC Sierra — Internal Mode Switch 'P' Circuit Stuck On Invalid Voltage Range

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 P18C2 GMC Code

1. What are the common symptoms of OBDII code P18C2 in a GMC vehicle?

- Common symptoms include issues with shifting gears, hesitation or jerking during acceleration, inability to start the vehicle, and the check engine light being illuminated.

2. What causes the Internal Mode Switch 'P' Circuit to be stuck on an invalid voltage range in a GMC vehicle?

- The most common causes of this issue are a malfunctioning internal mode switch, wiring or connection problems, a faulty transmission control module (TCM), or issues with the vehicle's power supply.

3. How can I diagnose the Internal Mode Switch 'P' Circuit issue in my GMC vehicle?

- To diagnose this problem, you can use an OBDII scanner to read the trouble codes, perform a visual inspection of the wiring and connections, test the internal mode switch for proper operation, and check the TCM for any faults.

4. Can I drive my GMC vehicle with the P18C2 code present?

- It is not recommended to drive a vehicle with the P18C2 code present, as it can lead to further damage to the transmission and other components. It is best to address the issue promptly.

5. What are some repair tips for fixing the Internal Mode Switch 'P' Circuit Stuck On Invalid Voltage Range in a GMC vehicle?

- Repair tips include checking and repairing any damaged wiring or connections, replacing the internal mode switch if necessary, resetting the TCM, and clearing the trouble codes with an OBDII scanner.

6. Is it possible to reset the P18C2 code without fixing the underlying issue in a GMC vehicle?

- While you can clear the trouble code temporarily, it is not recommended to reset the code without addressing the underlying problem, as it may lead to recurring issues and potential damage to the vehicle.

7. How much does it typically cost to repair the P18C2 code in a GMC vehicle?

- The cost of repairing the P18C2 code can vary depending on the root cause of the issue, the extent of the repairs needed, and the labor rates in your area. It is advisable to consult a mechanic for an accurate estimate.

8. Can a DIY enthusiast fix the Internal Mode Switch 'P' Circuit issue in a GMC vehicle?

- While some DIY enthusiasts may be able to diagnose and repair the issue themselves, it is recommended to have the problem addressed by a professional mechanic with experience in diagnosing and fixing transmission-related issues.

9. How long does it typically take to repair the P18C2 code in a GMC vehicle?

- The repair time for the P18C2 code can vary depending on the complexity of the issue and the availability of parts. In some cases, it may be a quick fix, while in others, it may take several hours or even days to fully resolve the problem.

10. Are there any preventive measures to avoid the Internal Mode Switch 'P' Circuit issue in a GMC vehicle?

- Regular maintenance, such as checking and replacing worn-out wiring or connections, keeping the TCM in good condition, and addressing any transmission-related issues promptly, can help prevent the occurrence of the P18C2 trouble code.