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.

Schematic Reference

Connector End View Reference

Component Connector End Views

Description and Operation

OnStar Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

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.

1. Ignition OFF, X1 harness connector at the audio amplifier.
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 3 (UX8)

•	Audio Common Circuit- terminal 19 (UX8)

•	Audio Signal Circuit- terminal 7 (UY5)

•	Audio Common Circuit- terminal 23 (UY5)

⇒	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 audio amplifier.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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