Buick Regal: DTC B127C

Diagnostic Instructions

• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Refer to Diagnostic Procedure Instructions provide an overview of each diagnostic category.

DTC Descriptors

DTC B127C 02

Microphone 2 Input Signal Circuit Short to Ground

DTC B127C 04

Microphone 2 Input Signal Circuit Open/High Resistance

Diagnostic Fault Information

Circuit/System Description

The radio provides the microphone 2 with a supplied voltage on the microphone high signal circuit.

When the microphone is in use, voice data from the user is sent back to the radio on the microphone low signal circuit. This microphone is used for driver side hands free calling enhancement, as well as a reference microphone for the primary microphone.

Conditions for Running the DTC

• The ignition must be in the RUN or ACC position/vehicle in Service Mode.
• The system voltage is at least 9.5 V and no more than 15.5 V.
• All the above conditions are present for greater than 5 s.

Conditions for Setting the DTC

B127C 02

The radio detects a short to ground in the microphone high signal circuit for 5 s or greater.

B127C 04

The following conditions will set this DTC:

• The radio detects an open/high resistance in the microphone high signal circuit for 10 s or greater.
• The radio detects an open/high resistance in the microphone low signal circuit for 10 s or greater.

Action Taken When the DTC Sets

• The radio will not receive a signal from the microphone.

Conditions for Clearing the DTC

• The condition responsible for setting the DTC no longer exists.
• A history DTC will clear once 50 consecutive malfunction-free ignition cycles have occurred.

Reference Information

Schematic Reference

Radio/Navigation System Wiring Schematics (IOB) , Radio/Navigation System Wiring Schematics (IOR) or Radio/Navigation System Wiring Schematics (IO5/IO6) , or Radio/Navigation System Wiring Schematics (IOS/IOT).

Connector End View Reference

Component Connector End View Index

Description and Operation

Radio/Audio System Description and Operation (IO6) , Radio/Audio System Description and Operation (IOB) , or Radio/Audio System Description and Operation (IOS/IOT/IOU).

Electrical Information Reference

• Refer to Circuit Testing
• Refer to Connector Repairs
• Refer to Testing for Intermittent Conditions and Poor Connections
• Refer to Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Testing

1. Ignition OFF/vehicle OFF, disconnect the harness connector at the B24 Cellular Phone Microphone, ignition ON/vehicle in Service Mode.

2. Test for 9-11 V between the signal circuit terminal 2 and ground.

• If less than 9 V

1. Ignition OFF/vehicle OFF, disconnect the X1 harness connector at the A11 Radio.
2. Test for infinite resistance between the signal circuit and ground.
   • If less than infinite resistance, repair the short to ground in the circuit.
   • Go to next step: If infinite resistance
3. Test for less than 2 Ω in the signal circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, replace the A11 Radio.

• If greater than 11 V

1. Ignition OFF/vehicle OFF, disconnect the X1 harness connector at the A11 Radio.
2. Test for less than 1 V between the signal circuit and ground.
   • If 1 V or greater, repair the short to voltage on the circuit.
   • Go to next step: If less than 1 V, replace the A11 Radio.

• Go to next step: If between 9-11 V

3. Test for less than 1 V between the low reference circuit terminal 1 and ground.

• If greater than 1 V

1. Ignition OFF/vehicle OFF, disconnect the X1 harness connector at the A11 Radio.
2. Test for less than 1 V between the low reference circuit and ground.
   • If 1 V or greater, repair the short to voltage in the circuit.
   • If less than 1 V, replace the A11 Radio

• Go to next step: If less than 1 V

4. Test for greater than 9 V between the signal circuit terminal 2 and the low reference circuit terminal 1.

• If less than 9 V

1. Ignition OFF/vehicle OFF, disconnect the X1 harness connector at the A11 Radio.
2. Test for infinite resistance between the low reference circuit and ground.
   • If less than infinite resistance, repair the short to ground in the circuit.
   • Go to next step: If infinite resistance
3. Test for less than 2 Ω in the signal circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, replace the A11 Radio.

• Go to next step: If greater than 9 V

5. Test or replace the B24 Cellular Phone Microphone.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• Refer to Mobile Telephone Microphone Replacement
• Refer to Control Module References for telematics communication interface control module replacement, programming and setup.

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