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
--- | --- | --- | --- | ---
Audio Signal | 1 | 1 | 1 | --
Audio Common Signal | -- | 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 audio signal and audio common 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 M

• | Audio Common Circuit- terminal L

⇒ | 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.