B2476

DTC B2476

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* 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/System Description

The OnStar(R) button assembly located on the inside rearview mirror 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 via the 10-volt reference circuit. Each of the buttons, when pressed, completes the circuit across a resister 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

The DTC will set when 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 100 consecutive malfunction-free ignition cycles have occurred.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the inside rearview mirror.
2. Ignition ON, test for 9.5-10.5 volts between the 10-volt reference circuit terminal 12 and ground.

^ If less than specified range, test the 10-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the CIM.
^ If greater than specified range, test the 10-volt reference circuit for a short to voltage. If the circuit tests normal, replace the CIM.

3. Test for less than 1 volt between the signal circuit terminal 11 ground.

^ If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the CIM.

4. Test for 9.5-10.5 volts between the 10-volt reference circuit terminal 12 and the signal circuit terminal 11.

^ If not within the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the CIM.

5. Ignition OFF, disconnect the X1 harness connector at the CIM.
6. Ignition OFF, test for infinite resistance between the signal circuit terminal 11 and ground.

^ If less than the specified value, test the signal circuit for a short to ground.

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

Repair Instructions

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

* Inside Rearview Mirror Replacement