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 00: Cellular Phone Select Service Switch
DTC B2482 00: 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 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. The communication interface module (CIM) supplies the OnStar® button assembly with 10 volts via 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 CIM over the keypad signal circuit. Depending upon the voltage range returned, the CIM is able to identify which button has been activated.

### Conditions for Running the DTC

• | Ignition ON.

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

### Conditions for Setting the DTC

#### B2476

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

#### B2482

The CIM 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 CIM will set this DTC.

### Action Taken When the DTC Sets

• | The OnStar® status LED turns red.

• | No calls can be placed.

• | The CIM 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 10 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. Ignition ON, test for less than 1 V 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 CIM.

4. Ignition OFF, test for 600 K - 800 K Ω 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. If the circuit tests normal, replace the CIM.

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

5. Ignition ON, test for 9.5-10.5 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 CIM.

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

6. 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 1.4 K - 1.6 K 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 2.7 K - 3.3 K 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 12.5 K - 13.5 K 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 CIM replacement, setup, and programming