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 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.

### Reference Information

#### Schematic Reference

OnStar Schematics

#### Connector End View Reference

Entertainment/Communication 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, With the scan tool command the VCIM to turn on the red and green LED.

⇒ | If the red or green LED indicators do not illuminate, go to Circuit/System Testing.

### Circuit/System Testing

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.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Control Module References for VCIM programming and setup

• | Inside Rearview Mirror Replacement