B2476

DTC B2476

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

DTC Descriptors
DTC B2476
- Cellular Phone Select Service Switch

Diagnostic Fault Information





Circuit/System Description

The OnStar(R) button assembly consists of 3 buttons, Call/Answer, OnStar(R) Call Center, and OnStar(R) Emergency. The communication interface module (CIM) supplies the OnStar(R) button assembly with 10 V 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 V.

Conditions for Setting the DTC

The CIM 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(R) status LED turns red.
* No calls can be placed.
* The CIM will ignore all inputs from the OnStar(R) button assembly.

Conditions for Clearing the DTC

* The condition responsible for setting the DTC no longer exists.
* A history DTC will clear once 50 consecutive malfunction-free ignition cycles have occurred.

Reference Information
Schematic Reference

OnStar Schematics (OnStar Schematics)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

OnStar Description and Operation (OnStar)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the OnStar switch.
2. Test for less than 5 Ohms between the ground circuit terminal 5 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 2 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 - 700 K Ohms between the keypad signal circuit terminal 2 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 9.8-10.2 V between the keypad supply voltage circuit terminal 4 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 OnStar switch.

Component Testing

1. Ignition OFF, disconnect the harness connector at the OnStar switch.
2. Test for infinite resistance between the keypad supply voltage terminal 4 and the keypad signal terminal 3.

• If less than the specified range, replace the OnStar switch.

3. Test for 1.4 K - 1.6 K Ohms between the keypad supply voltage terminal 4 and the keypad signal terminal 3 while pressing the black phone button.

• If not within the specified range, replace the inside OnStar switch.

4. Test for 2.7 K - 3.3 K Ohms between the keypad supply voltage terminal 4 and the keypad signal terminal 3 while pressing the blue On-Star(R) button.

• If not within the specified range, replace the inside OnStar switch.

5. Test for 2.7 K - 3.3 K Ohms between the keypad supply voltage terminal 4 and the keypad signal terminal 3 while pressing the red emergency button.

• If not within the specified range, replace the OnStar switch.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* OnStar Button Assembly Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for CIM replacement, setup, and programming