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 provide an overview of each diagnostic category.

### DTC Descriptor

DTC B2455 00: Cellular Phone Microphone Circuit

### Circuit/System Description

The vehicle communication interface module (VCIM) detects that the cellular microphone is connected through the cellular microphone signal circuit and the drain wire.

### 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 10 seconds.

### Conditions for Setting the DTC

• | The VCIM detects an open in the drain wire circuit or a short to voltage in the cellular microphone signal circuit.

• | The above conditions are present for greater than 10 seconds.

### Action Taken When the DTC Sets

• | The VCIM will not receive any signal from the microphone.

• | Calls can be placed but the caller cannot be heard.

• | The OnStar® status LED turns red.

### Conditions for Clearing the DTC

• | The VCIM detects the microphone connected for 5 consecutive 100 millisecond cycles.

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

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

### 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 harness connector at the cellular microphone.
2. Ignition ON, test for 9 - 11 volts at signal circuit terminal B.

⇒ | If greater than specified value, repair short to B+ or replace the VCIM.

⇒ | If less than specified value, repair short to ground or open/high resistance or replace the VCIM.

3. Disconnect the VCIM C2 harness connector.
4. Test for less than 1 volt at the cellular microphone terminal A .

⇒ | If greater than specified value, repair short to B+.

5. Test for greater than 1 ohm of resistance between terminal A and ground

⇒ | If less than specified value, repair short to ground.

6. Test for less than 1 ohm of resistance between terminal A and terminal 10.

⇒ | If greater than the specified value, repair open/high resistance.

7. If all circuits test normal, test or replace the cellular microphone.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Control Module References for VCIM replacement, setup, and programming

• | Mobile Telephone Microphone Replacement