AutoCodes – GMC – P18BB 2017 GMC Sierra

P18BB 2017 GMC Sierra Code - Internal Mode Switch 'B' 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: P18BB 2017 GMC Sierra indicates Internal Mode Switch 'B' 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 153

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 P18BB 2017 GMC Sierra 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 has an invalid voltage range of 1.68 – 2.38 V for 2.7 s.

OBDII Code P18BB 2017 GMC Sierra - Internal Mode Switch 'B' Circuit Stuck Off Invalid Voltage Range - AutoCodes.com — P18BB 2017 GMC Sierra Code - Internal Mode Switch 'B' Circuit Stuck Off Invalid Voltage Range

What does this mean?

What are the Possible Causes of the DTC P18BB 2017 GMC Sierra?

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 P18BB 2017 GMC Sierra?

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 P18BB 2017 GMC Sierra 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 P18BB 2017 GMC Sierra code?

Need more information on how to fix the P18BB 2017 GMC Sierra 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 P18BB 2017 GMC Sierra Code

1. What does the OBDII code P18BB mean on a 2017 GMC Sierra?

The P18BB code indicates an issue with the Internal Mode Switch 'B' Circuit, specifically that it is stuck off or has an invalid voltage range.

2. What are the common symptoms of the P18BB code in a GMC Sierra?

Symptoms may include difficulty shifting gears, the transmission being stuck in a specific gear, a check engine light, or erratic transmission behavior.

3. What causes the P18BB code to appear?

Common causes include a faulty internal mode switch, damaged wiring or connectors in the transmission control circuit, or a malfunctioning transmission control module (TCM).

4. Can a faulty internal mode switch trigger the P18BB code?

Yes, a malfunctioning or stuck internal mode switch is a primary cause of this error code.

5. Is it safe to drive with the P18BB code active?

Driving with this code can lead to transmission issues like improper gear engagement, so itâ€™s best to address the issue promptly to avoid further damage.

6. How do you diagnose the P18BB code in a 2017 GMC Sierra?

Diagnosis typically involves scanning for additional codes, inspecting the internal mode switch and wiring, and testing the voltage and continuity of the circuit.

7. What repairs are needed to fix the P18BB code?

Repairs may include replacing the internal mode switch, repairing or replacing damaged wiring, or reprogramming or replacing the transmission control module.

8. Can a software update fix the P18BB code?

In some cases, a TCM software update from the manufacturer may resolve the issue if itâ€™s related to a programming fault.

9. How much does it cost to fix the P18BB code on a GMC Sierra?

Repairs can range from $150 to $1,000 or more, depending on whether the issue is related to wiring, the internal mode switch, or the TCM.

10. Can I fix the P18BB code myself?

If you have experience with automotive diagnostics and repairs, you may be able to inspect wiring and replace the internal mode switch. However, more complex issues like TCM programming may require professional assistance.