AutoCodes – Chevrolet – P18B8 2018 Chevrolet Silverado

P18B8 2018 Chevrolet Silverado Code - Internal Mode Switch 'P' Circuit Shorted

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: P18B8 2018 Chevrolet Silverado indicates Internal Mode Switch 'P' Circuit Shorted.
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 334

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 P18B8 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 the internal mode switch P signal circuit voltage is between 0.966–1.68 V, for 1.75 s.

OBDII Code P18B8 2018 Chevrolet Silverado - Internal Mode Switch 'P' Circuit Shorted - AutoCodes.com — P18B8 2018 Chevrolet Silverado Code - Internal Mode Switch 'P' Circuit Shorted

What does this mean?

What are the Possible Causes of the DTC P18B8 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 P18B8 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 P18B8 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 P18B8 2018 Chevrolet Silverado code?

Need more information on how to fix the P18B8 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 P18B8 2018 Chevrolet Silverado Code

1. What does the OBDII code P18B8 mean on a 2018 Chevrolet Silverado?

Code P18B8 indicates a problem with the Internal Mode Switch (IMS) 'P' Circuit, specifically a shorted condition in the parking position circuit.

2. What are the common symptoms of code P18B8 in a 2018 Chevrolet Silverado?

Symptoms may include difficulty shifting into or out of Park, the transmission not engaging properly, or the check engine light being illuminated.

3. What causes the P18B8 code to appear?

The code is typically caused by a short in the IMS 'P' circuit, damaged wiring, a faulty Internal Mode Switch, or a malfunctioning transmission control module (TCM).

4. How can I diagnose the P18B8 code on my Silverado?

Begin by checking the wiring and connectors around the Internal Mode Switch for damage or corrosion. Use a multimeter to test for shorts or opens in the circuit and verify the IMS functionality.

5. Can the P18B8 code cause transmission failure?

While the code itself doesnâ€™t directly cause transmission failure, it can lead to improper gear engagement, which might stress the transmission over time if not addressed.

6. How do I fix the P18B8 code on a 2018 Chevrolet Silverado?

Repairs may involve fixing or replacing damaged wiring, cleaning or replacing corroded connectors, or replacing the Internal Mode Switch if it's faulty.

7. Is it safe to drive with the P18B8 code active?

Itâ€™s not recommended to drive for extended periods with this code active, as improper gear engagement can lead to unsafe driving conditions or further damage.

8. How much does it cost to repair the P18B8 code?

Repair costs can vary depending on the root cause but typically range from $100 to $400, including labor and parts, if the issue is with the wiring or the Internal Mode Switch.

9. Can I clear the P18B8 code without making repairs?

You can clear the code with an OBDII scanner, but it will likely return if the underlying issue isnâ€™t addressed.

10. Do I need a mechanic to fix the P18B8 code?

While some DIYers can handle basic wiring repairs, diagnosing and replacing the Internal Mode Switch or addressing more complex electrical issues may require professional assistance.