AutoCodes – GMC – B127C GMC

B127C GMC Code - Microphone 2 Input Signal Circuit

Quick Answer

The active noise cancellation system uses three microphones in the vehicle headliner: one above each front seating position, and one above the rear seat. Common causes include Faulty Radio Volume Compensator Interior Noise Microphone, Radio Volume Compensator Interior Noise Microphone harness is open or shorted, Radio Volume Compensator Interior Noise Microphone circuit poor electrical connection. Severity is Low - monitor the vehicle and repair when practical. The vehicle can usually be driven if no severe symptoms are present, but symptoms should be checked before extended driving.

What it means: B127C GMC indicates Microphone 2 Input Signal Circuit.
Common causes: Common causes include Faulty Radio Volume Compensator Interior Noise Microphone, Radio Volume Compensator Interior Noise Microphone harness is open or shorted, Radio Volume Compensator Interior Noise Microphone circuit poor electrical connection.
Severity: Low - monitor the vehicle and repair when practical.
Can I drive?: The vehicle can usually be driven if no severe symptoms are present, but symptoms should be checked before extended driving.

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Code Popularity 965

How popular is this code, among other codes? Low

Repair Importance Level

Low (Monitor) (1 / 3)

Repair Difficulty Level

Intermediate (2 / 3)

What is this?

Table of contents Created and updated by William Orellana on Nov 29, 2024

Description
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code B127C GMC Description

The active noise cancellation system uses three microphones in the vehicle headliner: one above each front seating position, and one above the rear seat. The Audio Amplifier provides a bias voltage to each microphone (+) and (-) signal circuit for the operation of the microphone. The microphones monitor the vehicle cabin for undesirable engine sounds. The Audio Amplifier uses the microphone inputs and an engine RPM signal to determine the frequency of the undesirable sound. The Diagnostic Trouble Code (DTC) will be set when a fault is detected on the specified (+) or (−) signal circuit for more than 1.5 seconds.

OBDII Code B127C GMC - Microphone 2 Input Signal Circuit - AutoCodes.com — B127C GMC Code - Microphone 2 Input Signal Circuit

What does this mean?

What are the Possible Causes of the DTC B127C GMC?

Faulty Radio Volume Compensator Interior Noise Microphone
Radio Volume Compensator Interior Noise Microphone harness is open or shorted
Radio Volume Compensator Interior Noise Microphone circuit poor electrical connection
Faulty Audio Amplifier

How to Fix the DTC B127C 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 does this mean?

Code Tech Notes

Installation of aftermarket replacement speakers, additional speakers/subwoofers, or aftermarket exhaust systems can cause undesirable behavior of the active noise cancellation system. The noise reduction microphones have foam blocks above them to seal the microphones and aid in the reduction of headliner vibration. Missing or out of place foam blocks can impact system performance.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the B127C 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 B127C GMC code?

Need more information on how to fix the B127C GMC code? Get Access to Factory Service Manuals

Need Help with the Code?

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Information for Specific GMC Models

B127C 2014 GMC Sierra — Microphone 2 Input Signal Circuit
B127C 2015 GMC Sierra — Microphone 2 Input Signal Circuit
B127C 2016 GMC Sierra — Microphone 2 Input Signal Circuit
B127C 2017 GMC Sierra — Microphone 2 Input Signal Circuit
B127C 2018 GMC Sierra — Microphone 2 Input Signal Circuit

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 B127C GMC Code

1. What does the OBDII code B127C on a GMC mean?

The B127C code indicates an issue with the Microphone 2 Input Signal Circuit, typically related to the communication system in the vehicle.

2. What are the common symptoms of the B127C code?

Symptoms may include poor microphone audio quality, failure of voice recognition features, or inoperative hands-free calling.

3. What causes the B127C code to appear on a GMC vehicle?

Common causes include a faulty microphone, damaged wiring or connectors, or a malfunction in the infotainment system.

4. Can I still drive my GMC with the B127C code?

Yes, this code does not affect drivability, but hands-free calling or voice recognition features may not function correctly.

5. How do I diagnose the B127C code in my GMC?

Start by inspecting the microphone and its wiring for visible damage. Use a scan tool to check for related codes and verify the signal from Microphone 2.

6. What is Microphone 2 in a GMC vehicle?

Microphone 2 typically refers to the secondary microphone used for hands-free communication or noise cancellation in certain GMC models.

7. How can I fix the B127C code on my GMC?

Repairs may involve replacing the faulty microphone, repairing damaged wiring or connectors, or updating the infotainment system software.

8. How much does it cost to repair the B127C code?

Repair costs vary, but replacing a microphone typically ranges from $50 to $200, plus labor charges if professional help is needed.

9. How can I prevent the B127C code from returning?

Ensure the microphone and wiring are free from damage, avoid physical impact to the headliner, and keep the infotainment system software updated.

10. Do I need a professional mechanic to fix the B127C code?

If you're comfortable with basic electrical diagnostics, you may be able to fix it yourself. Otherwise, a professional mechanic or dealership can assist.