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.

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Cellular Telephone Voice Signal | 1 | 1 | 1 | --
Cellular Telephone Voice Low Reference | -- | 1 | -- | --
1. No (or Noisy) OnStar® Audio

### Circuit/System Description

When an OnStar® keypress is made, a serial data message is sent to the audio system to mute all radio functions and output OnStar® originated audio. After the audio system is muted, the communication interface module (CIM) transmits signals to the audio system on the cellular telephone voice signal and cellular telephone voice low reference circuits.

### Reference Information

#### Schematic Reference

• | OnStar Schematics

• | Radio/Navigation System 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 Verification

1. Tune radio to a known good station and verify the audio is heard clearly through all speaker channels.

⇒ | If audio is not heard clearly, refer to Speaker Malfunction.

2. Ignition ON, radio ON, set volume to comfortable level and press OnStar® Call Center button. Verify Connecting to OnStar® message is heard clearly through the audio system.

⇒ | If OnStar® message is noisy or distorted, refer to Circuit/System Testing.

### Circuit/System Testing

1. Ignition OFF, disconnect the X2 harness connector at the radio.
2. Ignition ON, test for a varying AC voltage between the following signal circuit terminals listed below and ground when the OnStar® Call Center button is pressed.

• | Audio Signal Circuit- terminal 8

• | Audio Common Circuit- terminal 16

⇒ | If AC voltage was not present, test the circuit for a short to voltage, short to ground, or an open/high resistance. If the circuit tests normal, replace the CIM.

3. If all circuits test normal, replace the radio.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for radio or CIM replacement, setup, and programming.