AutoCodes – Generic – P18B6

P18B6 Code - Internal Mode Switch 'B' 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: P18B6 indicates Internal Mode Switch 'B' 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 1,986

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 P18B6 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 B signal circuit voltage is between 0.966–1.68 V, for 1.75 s.

OBDII Code P18B6 - Internal Mode Switch 'B' Circuit Shorted - AutoCodes.com — P18B6 Code - Internal Mode Switch 'B' Circuit Shorted

What does this mean?

What are the Possible Causes of the DTC P18B6?

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 P18B6?

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 P18B6 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

P18B6 Buick — Internal Mode Switch 'B' Circuit Shorted
P18B6 Cadillac — Internal Mode Switch 'B' Circuit Shorted
P18B6 Chevrolet — Internal Mode Switch 'B' Circuit Shorted
P18B6 GMC — Internal Mode Switch 'B' Circuit Shorted

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 P18B6 Code

1. What are common symptoms of OBDII code P18B6?

Common symptoms include issues with shifting gears, the inability to start the vehicle, and the transmission going into limp mode.

2. What are the possible causes of OBDII code P18B6?

The code P18B6 can be caused by a short circuit in the internal mode switch 'B' circuit, a faulty internal mode switch, or wiring issues.

3. How can I diagnose OBDII code P18B6?

Diagnosing this code typically involves using a scan tool to read the code, checking the internal mode switch 'B' circuit for shorts, and inspecting the wiring for any damage.

4. Can I still drive my vehicle with OBDII code P18B6?

It is not recommended to drive the vehicle with this code present, as it can lead to further transmission issues and potential safety hazards.

5. How can I repair OBDII code P18B6?

Repairing this code may involve replacing the internal mode switch, repairing any damaged wiring, or addressing the short circuit in the internal mode switch 'B' circuit.

6. Is OBDII code P18B6 a serious issue?

Yes, this code is considered serious as it affects the proper functioning of the transmission system, potentially leading to costly repairs if not addressed promptly.

7. Can a DIY enthusiast fix OBDII code P18B6 at home?

While some may attempt to diagnose and repair this code at home, it is recommended to seek professional help due to the complexity of transmission systems.

8. What should I do if OBDII code P18B6 keeps coming back after repairs?

If the code keeps reappearing after repairs, it indicates that the underlying issue has not been fully resolved, and further diagnosis is required to determine the root cause.

9. Are there any preventative measures to avoid OBDII code P18B6?

Regular maintenance of the transmission system, including checking for any signs of wiring damage or wear, can help prevent issues that may trigger this code.

10. How much does it typically cost to repair OBDII code P18B6 at a mechanic?

The cost of repairing this code can vary depending on the extent of the damage and the specific repairs needed, but it generally ranges from a few hundred to over a thousand dollars.