AutoCodes – Chevrolet – P18BF Chevrolet

P18BF Chevrolet Code - Internal Mode Switch 'A' 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: P18BF Chevrolet indicates Internal Mode Switch 'A' 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 1,215

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 P18BF Chevrolet 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 A signal circuit has an invalid voltage range of 0.70 – 0.96 V, for 2.7 s.

OBDII Code P18BF Chevrolet - Internal Mode Switch 'A' Circuit Stuck On Invalid Voltage Range - AutoCodes.com — P18BF Chevrolet Code - Internal Mode Switch 'A' Circuit Stuck On Invalid Voltage Range

What does this mean?

What are the Possible Causes of the DTC P18BF Chevrolet?

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 P18BF Chevrolet?

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 P18BF Chevrolet 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 Chevrolet Models

P18BF 2014 Chevrolet Silverado — Internal Mode Switch 'A' Circuit Stuck On Invalid Voltage Range
P18BF 2015 Chevrolet Silverado — Internal Mode Switch 'A' Circuit Stuck On Invalid Voltage Range
P18BF 2016 Chevrolet Silverado — Internal Mode Switch 'A' Circuit Stuck On Invalid Voltage Range
P18BF 2017 Chevrolet Silverado — Internal Mode Switch 'A' Circuit Stuck On Invalid Voltage Range
P18BF 2018 Chevrolet Silverado — Internal Mode Switch 'A' 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 P18BF Chevrolet Code

1. What does the OBDII code P18BF mean on a Chevrolet?

The P18BF code indicates that the Internal Mode Switch 'A' circuit is stuck in an invalid voltage range, which affects the transmission's ability to correctly interpret gear position.

2. What are the symptoms of code P18BF in a Chevrolet?

Common symptoms include the Check Engine Light turning on, erratic shifting, the vehicle being stuck in one gear, or the inability to shift gears.

3. What causes the P18BF code to appear?

The code is typically caused by a faulty internal mode switch, damaged wiring or connectors in the circuit, or internal transmission issues.

4. Can a faulty transmission control module (TCM) cause the P18BF code?

Yes, a malfunctioning TCM can cause this code if it fails to correctly process voltage signals from the internal mode switch.

5. How can I diagnose the P18BF code on my Chevrolet?

Start by inspecting the wiring and connectors for damage or corrosion, then use a multimeter to check for voltage inconsistencies in the switch circuit. Finally, scan the TCM for additional codes.

6. Is it safe to drive with the P18BF code active?

Driving with this code is not recommended, as it can lead to transmission failure, poor performance, or unsafe driving conditions.

7. How do I fix the P18BF code on my Chevrolet?

The repair may involve replacing the internal mode switch, repairing damaged wiring, or reprogramming or replacing the TCM if necessary.

8. How much does it cost to repair the P18BF code?

Repair costs vary but can range from $150 to $500 for parts and labor, depending on whether the internal mode switch or TCM needs replacement.

9. Can a low battery cause the P18BF code?

A low or failing battery can sometimes cause electrical issues but is unlikely to cause this specific code. However, ensuring proper battery voltage is still important.

10. Will clearing the P18BF code solve the issue?

Clearing the code without addressing the underlying issue will only temporarily turn off the Check Engine Light. The code will likely return until the root cause is fixed.