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 OnStar® button assembly consists of 3 buttons, Call/Answer, OnStar® Call Center, and OnStar® Emergency. Ten volts is supplied to the button assembly on the keypad supply voltage circuit. Each of the buttons, when pressed, completes the circuit across a resister allowing a specific voltage to be returned to the vehicle communication interface module (VCIM) on the keypad signal circuit. Depending upon the voltage range returned, the VCIM is able to identify which button has been pressed.

### 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

All Onstar® keypad buttons should operate normally when pressed.

### Circuit/System Testing (One or More Buttons Inoperative)

If some OnStar® buttons are inoperative but not all, replace the inside rearview mirror.

### Circuit/System Testing (All Buttons Inoperative)

1. Ignition OFF, disconnect the harness connector at the inside rearview mirror.
2. Ignition ON, test for 9.8-10.2 volts between the keypad supply voltage circuit terminal 6 and ground.

⇒ | If less or more than the specified value, repair short to ground, open or replace the VCIM.

3. Ignition OFF, reconnect the harness connector at the inside rearview mirror.
4. Disconnect the C1 VCIM harness connector.
5. Test for 500 to 20K ohms of resistance between C1 VCIM harness connector terminal 12 and 11 when each of the keypad button is pressed.

⇒ | If resistance is within the specified value when any of the keys are pressed replace the VCIM.

6. Disconnect the harness connector at the inside rearview mirror.
7. Test for infinite resistance between the inside rearview mirror connector terminal 11 and ground.

⇒ | If less than infinite resistance repair short to ground on the keypad signal circuit.

8. Test for less than 1 ohm between the C1 VCIM connector terminal 11 and the inside rearview mirror connector terminal 11.

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

⇒ | If all circuits test normal, replace the keypad.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Inside Rearview Mirror Replacement

• | Control Module References for VCIM replacement, setup, and programming