AutoCodes – Chevrolet – P18C3 2018 Chevrolet Silverado

P18C3 2018 Chevrolet Silverado 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 2018 Chevrolet Silverado 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 302

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 2018 Chevrolet Silverado 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 2018 Chevrolet Silverado - Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range - AutoCodes.com — P18C3 2018 Chevrolet Silverado Code - Internal Mode Switch 'S' Circuit Stuck On Invalid Voltage Range

What does this mean?

What are the Possible Causes of the DTC P18C3 2018 Chevrolet Silverado?

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 2018 Chevrolet Silverado?

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 2018 Chevrolet Silverado 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 P18C3 2018 Chevrolet Silverado code?

Need more information on how to fix the P18C3 2018 Chevrolet Silverado 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 P18C3 2018 Chevrolet Silverado Code

1. What does the OBDII code P18C3 mean on a 2018 Chevrolet Silverado?

The P18C3 code indicates that the Internal Mode Switch 'S' Circuit is stuck on an invalid voltage range, which could affect the transmission's ability to shift properly.

2. What are the common symptoms of the P18C3 code in a Chevy Silverado?

Symptoms may include difficulty shifting gears, the transmission stuck in one gear, reduced engine performance, or the Check Engine Light being illuminated.

3. What causes the P18C3 code to appear on a 2018 Chevrolet Silverado?

The P18C3 code can be caused by a faulty internal mode switch, damaged wiring or connectors in the mode switch circuit, a malfunctioning transmission control module (TCM), or corrosion in the circuit.

4. Can I still drive my 2018 Chevrolet Silverado with the P18C3 code?

While the truck may still be drivable, it is not recommended to continue driving with this code as it can lead to further transmission issues or unsafe driving conditions.

5. How is the P18C3 code diagnosed on a Chevy Silverado?

A mechanic will use a scan tool to retrieve the code, inspect the internal mode switch and related wiring for damage or corrosion, and test the voltage and continuity of the circuit.

6. What repairs are typically needed to fix the P18C3 code?

Repairs may include replacing the internal mode switch, repairing or replacing damaged wiring or connectors, cleaning corrosion, or reprogramming or replacing the transmission control module (TCM).

7. How much does it cost to fix the P18C3 code on a 2018 Chevrolet Silverado?

The cost can vary depending on the specific repair needed. Replacing an internal mode switch typically costs $200â€“$500, while wiring repairs may cost less. A TCM replacement could exceed $1,000.

8. Can a P18C3 code be caused by low transmission fluid?

Low transmission fluid is not a direct cause of the P18C3 code, but it can exacerbate transmission issues, so checking and maintaining proper fluid levels is important.

9. Can I reset the P18C3 code without repairing it?

You can clear the code using an OBDII scan tool, but if the underlying issue isnâ€™t resolved, the code will likely return, and the symptoms may persist or worsen.

10. Is the P18C3 code a common issue for 2018 Chevrolet Silverado trucks?

While not extremely common, this code can occur in Silverado models, especially if there is wear and tear on the internal mode switch or issues in the transmission wiring. Regular maintenance can help prevent it.