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OnStar Microphone Malfunction

OnStar Microphone Malfunction

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.

• Diagnostic Procedure Instructions provides an overview of each diagnostic category.


Diagnostic Fault Information

Circuit Short to Ground Open/High Resistance Short to Voltage Signal Performance
Cellular Microphone Signal B2455 02 B2455 04 - -
Cellular Microphone Low Reference - B2455 04 1 -
1. OnStar Microphone Inoperative - Caller Cannot Be Heard


Circuit/System Description

The telematics communication interface control module provides the cellular phone microphone with a supplied voltage on the cellular phone microphone signal circuit. When the cellular phone microphone is in use, voice data from the user is sent back to the telematics communication interface control module on the signal circuit. The telematics communication interface control module provides a ground for the microphone via the low reference wire.

Reference Information

Schematic Reference

OnStar Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

OnStar Description and Operation

Electrical Information Reference


• Circuit Testing

• Connector Repairs

• Testing for Intermittent Conditions and Poor Connections

• Wiring Repairs


Scan Tool Reference

Control Module References for scan tool information

Circuit/System Testing


1. Ignition OFF, disconnect the harness connector at the B24 cellular phone microphone.

2. Ignition ON, test for 9.5-10.5 V between the signal circuit terminal B and ground.

3. If less than the specified range, test the circuit for a short to ground, shorted together, or an open/high resistance. If the circuit tests normal, replace the K73 telematics communication interface control module.

4. If greater than the specified range, test the circuit for a short to voltage. If the circuit tests normal, replace the K73 telematics communication interface control module.

5. Test for 9.5-10.5 V between the signal circuit terminal B and the low reference circuit terminal A.

6. If less than the specified range, test the low reference circuit for a short to ground, shorted together, or an open/high resistance. If the circuit tests normal, replace the K73 telematics communication interface control module.

7. If greater than the specified range, test the low reference circuit for a short to voltage. If the circuit tests normal, replace the K73 telematics communication interface control module.

8. If all circuit test normal, replace the B24 cellular phone microphone.


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.


• Mobile Telephone Microphone Replacement

• Control Module References for telematics communication interface control module replacement, setup, and programming