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 vehicle navigation radio and OnStar® system both utilize the cellular microphone to receive voice commands. The navigation radio receives an audio voice signal from the communication interface module (CIM).

### Reference Information

#### Schematic Reference

Radio/Navigation System Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Radio/Audio System 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

Ignition ON, verify the OnStar® voice recognition is operating normally.

⇒ | If the OnStar® voice recognition is inoperative, refer to OnStar Microphone Inoperative - Caller Cannot Be Heard .

### Circuit/System Testing

1. Ignition OFF, disconnect the X2 harness connector at the CIM.
2. Ignition ON, test for 8.5-9.5 volts between the mono out signal circuit terminal 1 and ground.

⇒ | If less than specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the radio.

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

3. Ignition OFF, test for less than 10 ohms between the mono out low reference circuit terminal 2 and ground.

⇒ | If greater than the specified range, test the low reference circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the radio.

4. Ignition ON, test for 8.5-9.5 volts between the mono out signal circuit terminal 1 and the drain wire circuit terminal 8.

⇒ | If less than specified range, test the drain wire circuit for a short to voltage or an open/high resistance.

5. Ignition OFF, disconnect the X2 harness connector at the radio.
6. Verify that a test lamp does not illuminate between B+ and the mono out low reference circuit terminal 15.

⇒ | If the test lamp illuminates, test the low reference circuit for a short to ground.

7. If all circuits test normal, replace the CIM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for Radio or CIM replacement, setup, and programming