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 radio is supplied with OnStar® a mono audio from vehicle communication interface module (VCIM). When the radio receives an audio signal from the VCIM the radio mutes the current audio signal and delivers an audio signal from the OnStar® system.

### 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

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

⇒ | If audio is not heard clearly refer to Diagnostic Starting Point - Cellular, Entertainment, and Navigation .

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

⇒ | If OnStar® message is not heard, go to Circuit/System Testing (No OnStar® Audio).

⇒ | If OnStar® message is noisy or distorted, go to Circuit/System Testing (Noisy OnStar® Audio).

### Circuit/System Testing (No OnStar® Audio)

1. Ignition OFF, disconnect the C2 radio harness connector.
2. Ignition ON, test for a momentary AC voltage (OnStar® audio signal) between the C2 connector terminal cavity 8 and 16 when the white dot button on the keypad is pressed.

⇒ | If a momentary AC voltage was present replace the radio.

3. Ignition OFF, disconnect the C2 VCIM harness connector.
4. Test for less than 1 ohm between the C2 VCIM connector terminal 1 and the radio C2 connector terminal 8.

⇒ | If more than the specified value repair open or high resistance on the cellular telephone signal circuit.

5. Test for less than 1 ohm between the C2 VCIM connector terminal 2 and the radio C2 connector terminal 16.

⇒ | If more than the specified value repair open or high resistance on the cellular telephone signal circuit.

6. If all circuits test normal, replace the VCIM.

### Circuit/System Testing (Noisy OnStar® Audio)

1. Ignition OFF, disconnect the C2 radio harness connector.
2. Disconnect the C2 VCIM harness connector.
3. Test for less than 1 volt between the C2 VCIM connector terminal 1 and the radio C2 connector terminal 8.

⇒ | If more than the specified value repair short to voltage on the cellular telephone voice signal circuit.

4. Test for less than 1 volt between the C2 VCIM connector terminal 2 and the radio C2 connector terminal 16.

⇒ | If more than the specified value repair short to voltage on the cellular telephone voice low reference circuit.

5. Test for infinite resistance between the C2 VCIM connector terminal 1 and 2 and ground.

⇒ | If less than infinite resistance repair short to ground on the cellular telephone voice signal circuit or cellular telephone voice low reference circuit.

6. If all circuits test normal, replace the VCIM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for radio and VCIM programming and setup