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.

### DTC Descriptors

DTC B2476: Cellular Phone Select Service Switch
DTC B2482: Cellular Phone Select Service Switch Range/Performance

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Keypad Supply Voltage | B2476 | B2476 | B2476 | --
Keypad Green LED Signal | 1 | 1 | 2 | --
Keypad Red LED Signal | 1 | 1 | 2 | --
Keypad Signal | 3 | 3 | -- | B2482
Inside Rearview Mirror Ground | -- | 1 | -- | --
1. OnStar® LED Inoperative 2. LED Illuminated At All Times 3. OnStar® Buttons Inoperative

### Circuit/System Description

The OnStar® button assembly consists of 3 buttons: Call/Answer, OnStar® Call Center, and OnStar® Emergency. The vehicle communication interface module (VCIM) supplies the OnStar® button assembly with 10 volts via the keypad 10 volt reference circuit. Each of the buttons, when pressed, completes the circuit across a resistor allowing a specific voltage to be returned to the VCIM over the keypad signal circuit. Depending upon the voltage range returned, the VCIM is able to identify which button has been activated.

### Conditions for Running the DTC

• | Ignition ON.

• | Battery voltage is between 9-16 volts.

### Conditions for Setting the DTC

#### DTC B2476

The VCIM detects a short to voltage, short to ground, or an open/high resistance on the keypad supply voltage circuit.

#### DTC B2482

The VCIM detects a valid signal on the keypad signal circuit for longer than 15 seconds. If one of the OnStar® buttons is held or stuck for 15 seconds or greater, the VCIM will set this DTC.

### Action Taken When the DTC Sets

• | The OnStar® status LED turns red.

• | No calls can be placed.

• | The VCIM will ignore all inputs from the OnStar® button assembly.

### Conditions for Clearing the DTC

• | The condition responsible for setting the DTC no longer exists.

• | A history DTC will clear once 100 consecutive malfunction-free ignition cycles have occurred.

### Reference Information

#### Schematic Reference

OnStar Schematics

#### Connector End View Reference

Component 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

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the inside rearview mirror.
2. Test for less than 5 Ω between the mirror ground circuit terminal 8 and ground.

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

3. Ignition ON, test for less than 1 volt between the keypad signal circuit terminal 11 and ground.

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

4. Ignition OFF, test for 600 K - 700 K Ω between the keypad signal circuit terminal 11 and ground.

⇒ | If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the VCIM.

⇒ | If greater than the specified range, test the signal circuit for an open/high resistance. If the circuit tests normal, replace the VCIM.

5. Ignition ON, test for 9.8-10.2 V between the keypad supply voltage circuit terminal 12 and ground.

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

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

6. If all circuits test normal, test or replace the inside rearview mirror.

### Component Testing

1. Ignition OFF, disconnect the harness connector at the inside rearview mirror.
2. Test for infinite resistance between the supply voltage terminal 12 and the signal terminal 11.

⇒ | If not the specified value, replace the inside rearview mirror.

3. Test for 1.4k-1.6k ohms between the supply voltage terminal 12 and the signal terminal 11 while pressing the black Call/Answer button.

⇒ | If not within the specified range, replace the inside rearview mirror.

4. Test for 2.7k-3.3k ohms between the supply voltage terminal 12 and the signal terminal 11 while pressing the blue On-Star® button.

⇒ | If not within the specified range, replace the inside rearview mirror.

5. Test for 11.7k-14.3k ohms between the supply voltage terminal 12 and the signal terminal 11 while pressing the red emergency button.

⇒ | If not within the specified range, replace the inside rearview mirror.

### 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