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 Descriptor

DTC B2476 00 : Cellular Phone Select Service Switch Malfunction

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Keypad Supply Voltage | B2476 00 | B2476 00 | B2476 00 | --
Keypad Green LED Signal | 1 | 1 | 2 | --
Keypad Red LED Signal | 1 | 1 | 2 | --
Keypad Signal | 3 | 3 | -- | B2482 00
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. 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 resistor 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.

### Conditions for Running the DTC

• | Ignition ON.

• | Battery voltage must be between 9-16 volts.

### Conditions for Setting the DTC

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

### 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 clears after 50 malfunction-free ignition cycles.

### 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 Testing

1. Ignition OFF, disconnect the VCIM C1 harness connector and 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 ground circuit for an open/high resistance.

3. Test for infinite resistance between the keypad signal circuit terminal 11 and ground.

⇒ | If less than the specified range, test the keypad signal circuit for a short to ground.

4. Reconnect the VCIM C1 harness connector.
5. Ignition ON, test for 0 volt between the keypad signal circuit terminal 11 and ground.

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

6. Test for 9.8-10.2 volts 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.

7. Test for 9.8-10.2 volts between the keypad supply voltage circuit terminal 12 and the keypad signal circuit terminal 11.

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

8. If all circuits test normal, test or replace the button assembly.

### Component Testing

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

⇒ | If less than the specified range, replace the inside rearview mirror.

3. Test for 1.4k-1.6k Ω between the keypad supply voltage terminal 12 and the keypad signal terminal 11 while pressing the black phone button.

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

4. Test for 2.7k-3.3k Ω between the keypad supply voltage terminal 12 and the keypad 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 Ω between the keypad supply voltage terminal 12 and the keypad 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