The vehicle communication interface module (VCIM) commands on the red or green LED by supplying ground to either the keypad red signal circuit or keypad green signal circuit.

Schematic Reference

OnStar Schematics

Connector End View Reference

Entertainment/Communication Connector End Views

Description and Operation

OnStar Description and Operation

Electrical Information Reference

Ignition ON, With the scan tool command the VCIM to turn on the red and green LED.

1. Ignition OFF, disconnect the inside rearview mirror harness connector .
2. Ignition ON, test for 9.2 to 10.2 volts on the keypad supply voltage circuit.

⇒	If less than the specified voltage repair short to ground or open or replace the VCIM.

3. Test for less than 1 ohm between the inside rearview mirror harness connector terminal 8 and ground.

⇒	If greater than specified value repair open or high resistance.

4. Connect a DMM between the inside rearview mirror harness connector terminal 14 and ground. With a scan tool command the green LED ON. Verify 9.2 to 10.2 volts is present with the green LED commanded ON.

⇒	If 9.2 to 10.2 volts is present with the green LED is commanded ON, replace the inside rearview mirror.

5. Connect a DMM between the inside rearview mirror harness connector terminal 15 and ground. With a scan tool command the green LED ON. Verify 9.2 to 10.2 volts is present with the red LED commanded ON.

⇒	If 9.2 to 10.2 volts is present with the red LED is commanded ON, replace the inside rearview mirror.

6. Disconnect the VCIM harness connector C1.
7. Test for less than 1 volt between the C1 VCIM connector terminal 3 and the inside rearview mirror harness connector terminal 14.

⇒	If more than the specified value repair short to voltage on the keypad green LED signal circuit.

8. Test for less than 1 volt between the C1 VCIM connector terminal 2 and the inside rearview mirror harness connector terminal 15.

⇒	If more than the specified value repair short to voltage on the keypad red LED signal circuit.

9. Test for less than 1 ohm between the C1 VCIM connector terminal 3 and the inside rearview mirror harness connector terminal 14.

⇒	If more than the specified value repair open or high resistance on the keypad green LED signal circuit.

10. Test for less than 1 ohm between the C1 VCIM connector terminal 2 and the inside rearview mirror harness connector terminal 15.

⇒	If more than the specified value repair open or high resistance on the keypad red LED signal circuit.

11. If all circuits test normal, test or replace the VCIM.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.