For 1990-2009 cars

### Circuit Description

The OnStar® button assembly consists of 3 buttons, Call/Answer, OnStar® Call Center, and OnStar® Emergency. Ten volts are supplied to the button assembly on the keypad supply voltage circuit. Each of the buttons, when pressed, complete the circuit across a resister 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.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B2476 Cellular Phone Select Service Switch Malfunction (3 button assembly)

### Conditions for Running the DTC

• | The ignition must be in the RUN or ACC position.

• | The system voltage is at least 9.5 volts and no more than 15.5 volts.

• | All the above conditions are present for greater than 300 milliseconds.

### Conditions for Setting the DTC

• | The VCIM powers the button assembly through the keypad supply voltage circuit for 11.5 milliseconds, turns the power off, then waits for 50 milliseconds and sees a voltage value greater than 1.8 volts on this circuit.

• | The above conditions are present for greater than 300 milliseconds.

### Action Taken When the DTC Sets

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

• | No calls can be placed.

• | The OnStar® status LED turns RED.

### Conditions for Clearing the DTC

• | The VCIM powers the button assembly through the keypad supply voltage circuit for 11.5 milliseconds, turns the power off, then waits for 50 milliseconds and sees a voltage value less than 1.8 volts on this circuit.

• | A history DTC clears after 50 malfunction-free ignition cycles.

• | The VCIM receives the clear DTC command from the scan tool.

### Test Description

The number below refers to the step number on the diagnostic table.

1. This step checks that the VCIM is sending out the proper supply voltage.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: OnStar Schematics Connector End View Reference: Entertainment/Communication Connector End Views
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. Turn the ignition OFF.
2. Disconnect the rearview mirror assembly connector.
3. Turn the ignition ON, with the engine OFF.
4. Measure the voltage from the keypad supply voltage circuit to a good ground.

Does the voltage measure greater than the specified value?

9 V

Go to Step 4

Go to Step 3

3 | Test the keypad supply voltage circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 8
4 | Test the keypad supply voltage circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 5
5 | Test the keypad ground circuit for an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 6
6 | Test the keypad signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 7
7 | Inspect for poor connections at the harness connector of the rearview mirror. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 9
8 | Inspect for poor connections at the harness connector of the vehicle communication interface module (VCIM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10
9 | Replace the rearview mirror. Refer to Inside Rearview Mirror Replacement . Did you complete the replacement? | -- | Go to Step 11 | --
10 | Replace the VCIM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 11 | --
11 |

1. Use the scan tool in order to clear the DTCs.
2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK