AutoCodes – Generic – P18C2

P18C2 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 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 1,703

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

What does this mean?

What are the Possible Causes of the DTC P18C2?

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?

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 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.

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Information for Specific Makes

P18C2 Buick — Internal Mode Switch 'P' Circuit Stuck On Invalid Voltage Range
P18C2 Cadillac — Internal Mode Switch 'P' Circuit Stuck On Invalid Voltage Range
P18C2 Chevrolet — Internal Mode Switch 'P' Circuit Stuck On Invalid Voltage Range
P18C2 GMC — 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 Code

1. What are common symptoms of OBDII code P18C2?

The common symptoms of OBDII code P18C2 include issues with the vehicle's automatic transmission shifting, difficulty selecting gears, and the vehicle going into "limp mode."

2. What causes the Internal Mode Switch 'P' Circuit Stuck On Invalid Voltage Range code (P18C2)?

This code is usually triggered by a faulty internal mode switch (IMS), damaged wiring or connectors related to the IMS, or a malfunctioning transmission control module (TCM).

3. How can I diagnose the Internal Mode Switch 'P' Circuit Stuck On Invalid Voltage Range code (P18C2)?

Diagnosis involves using a scan tool to read the OBDII code, checking the wiring and connectors related to the internal mode switch, and testing the internal mode switch itself for proper voltage readings.

4. Can I still drive my vehicle with OBDII code P18C2 present?

It is not recommended to drive your vehicle with this code present, as it can lead to transmission issues and potentially cause further damage. It's best to address the underlying problem promptly.

5. How can I repair OBDII code P18C2 at home?

If you have the necessary tools and expertise, you can attempt to replace the internal mode switch or repair any damaged wiring or connectors yourself. However, it's recommended to consult a professional for accurate diagnosis and repair.

6. Is it safe to clear the OBDII code P18C2 without fixing the issue?

Clearing the code without addressing the underlying problem will only temporarily remove the check engine light. The issue causing the code will persist, potentially leading to more severe transmission problems in the future.

7. Will OBDII code P18C2 affect my vehicle's fuel efficiency?

While the code itself may not directly impact fuel efficiency, the underlying transmission issues associated with P18C2 can affect how efficiently your vehicle operates. It's best to address the problem promptly to maintain optimal performance.

8. Can a faulty internal mode switch cause other transmission-related issues?

Yes, a faulty internal mode switch can cause various transmission-related issues, such as erratic shifting, difficulty engaging gears, and transmission slipping. It's crucial to address the problem to prevent further damage.

9. How much does it typically cost to repair OBDII code P18C2 at a repair shop?

The cost of repairing OBDII code P18C2 can vary depending on the extent of the issue, the labor rates of the repair shop, and the cost of any necessary parts. It's advisable to obtain quotes from different shops for an accurate estimate.

10. How can I prevent OBDII code P18C2 from recurring in the future?

To prevent OBDII code P18C2 from recurring, ensure regular maintenance of your vehicle's transmission system, check for any signs of wear or damage in the internal mode switch and related components, and promptly address any transmission issues that arise.