For 1990-2009 cars

### 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.

### Circuit/System Description

The OnStar® vehicle communication interface module (VCIM) recieves an audio input signal from the cellular microphone.

### Reference Information

#### Schematic Reference

OnStar Schematics

#### Connector End View Reference

Entertainment/Communication 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

### Circuit/System Verification

Ignition ON, press OnStar® Call button. Verify that your voice cannot be heard clearly by the OnStar® Call Center.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the cellular microphone.
2. Ignition ON, test for greater than 9 volts between the signal circuit terminal B and ground.

⇒ | If less than specified value, test the cellular microphone signal circuit for a short to ground, open/high resistance. If the circuit tests normal, replace the VCIM.

3. Test for greater than 9 volts between the cellular microphone signal circuit terminal B and the drain circuit terminal A.

⇒ | If less than specified value, test the drain wire for an open/high resistance. If the circuit tests normal, replace the VCIM.

4. If all circuit test normal, test or replace the cellular microphone assembly.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Mobile Telephone Microphone Replacement

• | Control Module References for VCIM replacement, setup, and programming