The vehicle communication interface module (VCIM) provides the cellular microphone with a supplied voltage on the cellular microphone signal circuit. When the microphone is in use, voice data from the user is sent back to the VCIM on the signal circuit. The VCIM provides a ground for the microphone via the low reference circuit.

Schematic Reference

OnStar Schematics

Connector End View Reference

Cellular Communication Connector End Views

Description and Operation

OnStar Description and Operation

Electrical Information Reference

Scan Tool Reference

1. Ignition OFF, disconnect the harness connector at the cellular microphone.
2. Test for less than 10 Ω between the microphone low reference circuit and ground.

⇒	If greater than the specified range, test the circuit for an open/high resistance.

3. Ignition ON, test for 9.5-10.5 V between the microphone signal circuit and ground.

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

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

4. If all circuits test normal, replace the cellular microphone.