AutoCodes – Generic – P18C3

P18C3 Code - Internal Mode Switch 'S' 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: P18C3 indicates Internal Mode Switch 'S' 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 1,592

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 P18C3 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 has an internal mode switch S signal circuit has an invalid voltage range of 0.70 – 0.96 V, for 2.7 s.

OBDII Code P18C3 - Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range - AutoCodes.com — P18C3 Code - Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range

What does this mean?

What are the Possible Causes of the DTC P18C3?

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 P18C3?

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 P18C3 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

P18C3 Buick — Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range
P18C3 Cadillac — Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range
P18C3 Chevrolet — Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range
P18C3 GMC — Internal Mode Switch 'S' 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 P18C3 Code

1. What are common symptoms of OBDII code P18C3?

- Common symptoms of this code include issues with shifting gears, erratic transmission behavior, and possibly the vehicle going into limp mode.

2. What causes the Internal Mode Switch 'S' Circuit to be stuck on an invalid voltage range?

- The most common causes of this issue are a faulty internal mode switch, wiring or connection issues, or a malfunction in the transmission control module.

3. How serious is the Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range issue?

- This issue can affect the drivability of the vehicle and may lead to further transmission problems if not addressed promptly.

4. Can I continue driving with OBDII code P18C3 present?

- It is not recommended to continue driving with this code present, as it can potentially cause more damage to the transmission over time.

5. How can I diagnose the Internal Mode Switch 'S' Circuit issue?

- Diagnosing this issue typically involves using a scan tool to check for the specific trouble code and then conducting tests on the internal mode switch, wiring, and transmission control module.

6. Is it possible to repair the Internal Mode Switch 'S' Circuit issue myself?

- Repairing this issue may require specialized knowledge and tools, so it is usually best to have a qualified mechanic diagnose and fix the problem.

7. How much does it cost to repair OBDII code P18C3?

- The cost of repairing this issue can vary depending on the exact cause and the labor rates of the repair shop. It is recommended to get a few quotes from different mechanics.

8. Can a faulty internal mode switch be repaired, or does it need to be replaced?

- In most cases, a faulty internal mode switch will need to be replaced rather than repaired to ensure proper functioning of the transmission.

9. Will resetting the trouble code make the issue go away permanently?

- Resetting the trouble code may temporarily turn off the check engine light, but if the underlying issue is not fixed, the code will likely return.

10. How long does it typically take to repair the Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range issue?

- The repair time can vary depending on the exact cause of the problem and the availability of parts, but it is generally recommended to allow for at least a few hours of labor for diagnosis and repair.