AutoCodes – GMC – P18BD GMC

P18BD GMC Code - Internal Mode Switch 'P' Circuit Stuck Off 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: P18BD GMC indicates Internal Mode Switch 'P' Circuit Stuck Off 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 1,618

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 P18BD 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 1.68 – 2.38 V for 2.7 s.

OBDII Code P18BD GMC - Internal Mode Switch 'P' Circuit Stuck Off Invalid Voltage Range - AutoCodes.com — P18BD GMC Code - Internal Mode Switch 'P' Circuit Stuck Off Invalid Voltage Range

What does this mean?

What are the Possible Causes of the DTC P18BD 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 P18BD 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 P18BD 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 P18BD GMC code?

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Information for Specific GMC Models

P18BD 2014 GMC Sierra — Internal Mode Switch 'P' Circuit Stuck Off Invalid Voltage Range
P18BD 2015 GMC Sierra — Internal Mode Switch 'P' Circuit Stuck Off Invalid Voltage Range
P18BD 2016 GMC Sierra — Internal Mode Switch 'P' Circuit Stuck Off Invalid Voltage Range
P18BD 2017 GMC Sierra — Internal Mode Switch 'P' Circuit Stuck Off Invalid Voltage Range
P18BD 2018 GMC Sierra — Internal Mode Switch 'P' Circuit Stuck Off 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 P18BD GMC Code

1. What are the common symptoms of OBDII code P18BD GMC?

The common symptoms of code P18BD may include issues with shifting gears, the inability to start the vehicle, and the illumination of the Check Engine Light.

2. What are the possible causes of OBDII code P18BD GMC?

The possible causes of code P18BD include a faulty internal mode switch, damaged wiring harness, poor electrical connection, or a malfunctioning transmission control module.

3. How serious is OBDII code P18BD GMC?

Code P18BD can cause drivability issues and may lead to further transmission problems if left unresolved. It is recommended to address the issue promptly to prevent potential damage to the vehicle.

4. How can I diagnose OBDII code P18BD GMC?

Diagnosing code P18BD typically involves using a diagnostic scanner to retrieve the trouble codes and performing a thorough inspection of the internal mode switch, wiring, and connections for any signs of damage or malfunction.

5. Can I still drive my vehicle with OBDII code P18BD GMC?

It is not advisable to drive the vehicle with an active P18BD trouble code, as it may lead to further damage to the transmission system. It is recommended to address the issue and have the vehicle repaired before driving.

6. What are some repair tips for OBDII code P18BD GMC?

Repair tips for code P18BD may include inspecting and repairing any damaged wiring or connections, replacing the internal mode switch if necessary, and resetting the trouble codes after completing the repairs.

7. How much does it typically cost to repair OBDII code P18BD GMC?

The cost of repairing code P18BD can vary depending on the extent of the issue, the parts needed for replacement, and labor costs. It is recommended to consult with a professional mechanic for an accurate estimate.

8. Can a DIY enthusiast fix OBDII code P18BD GMC?

While some experienced DIY enthusiasts may be able to diagnose and repair code P18BD, it is recommended to seek the assistance of a qualified mechanic, especially when dealing with transmission-related issues.

9. Will resetting the trouble codes make OBDII code P18BD GMC go away?

Resetting the trouble codes may temporarily clear the Check Engine Light, but if the underlying issue causing code P18BD is not addressed, the code is likely to reappear once the vehicle is driven again.

10. How can I prevent OBDII code P18BD GMC from recurring?

To prevent code P18BD from recurring, it is essential to address any underlying issues promptly, conduct regular maintenance checks on the transmission system, and follow the manufacturer's recommended service intervals.