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

When an OnStar® keypress is made, the radio mute signal circuit is activated, sending a signal to the audio system to mute all radio functions and transmit OnStar® originated audio. With the audio system is muted, the OnStar® audio signal is transmitted to the audio system on the audio signal output circuit (+) and the audio common signal circuit (-).

### 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

### Circuit/System Verification

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

⇒ | If the radio does not mute, refer to OnStar Mute Malfunction.

⇒ | If the OnStar message is not heard, refer to OnStar Audio Malfunction.

### Circuit/System Testing

#### OnStar Mute Malfunction

1. Ignition OFF, disconnect the harness connector at the radio and the X2 harness connector at the VCIM.
2. Ignition ON, test for less than 1 volt between the signal circuit terminal 12 X2 and ground.

⇒ | If greater than the specified range, test the signal circuit for a short to voltage.

3. Test for infinite resistance between the signal circuit terminal 12 X2 and ground.

⇒ | If not the specified value, test the signal circuit for a short to ground.

4. Test for less than 1 ohm between the signal circuit terminal 12 at the VCIM and the signal circuit terminal 11 at the radio.

⇒ | If greater than the specified range, test the signal circuit for a short to ground.

5. If all circuits test normal, replace the VCIM.
6. Radio ON, set volume to comfortable level and press OnStar Center Call button. Verify the radio mutes.

⇒ | If the radio does not mute, replace the radio.

#### OnStar Audio Malfunction

1. Ignition OFF, disconnect the harness connector at the radio and the X2 harness connector at the VCIM.
2. Ignition ON, test for less than 1 volt between the following signal circuit terminals and ground:

• | VCIM signal circuit terminal 1

• | VCIM signal circuit terminal 2

Important: If the audio common circuit is shorted to voltage, the VCIM has been damaged and requires replacement.

⇒ | If greater than the specified range, test the signal circuit for a short to voltage.

3. Test for infinite resistance between the following signal circuit terminals and ground.

• | VCIM signal circuit terminal 1

• | VCIM signal circuit terminal 2

⇒ | If not the specified value, test the signal circuit for a short to ground.

4. Test for less than 1 ohm between the following signal circuit terminal:

• | VCIM signal circuit terminal 1 and radio signal circuit terminal 34

• | VCIM signal circuit terminal 2 and radio signal circuit terminal 40

⇒ | If greater than the specified range, test the signal circuit for a short to ground.

5. If all circuits test normal, replace the VCIM.
6. Radio ON, set volume to comfortable level and press OnStar Center Call button. Verify the "Connecting to OnStar" message is heard clearly through the audio system.

⇒ | If the OnStar message is not heard, replace the radio.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for VCIM or radio replacement, setup, and programming