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: Cellular Phone Microphone Circuit Malfunction

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Cellular Microphone Signal | B2455 | B2455 | B2455 | --
Cellular Microphone Low Reference | -- | B2455 | -- | --

### Circuit/System Description

The vehicle communication interface module (VCIM) provides the cellular microphone with a supplied voltage on the cellular microphone signal circuit. When the microphone is in use, voice data from the user is sent back to the VCIM on the signal circuit. The VCIM provides a ground for the microphone via the low reference circuit.

### Conditions for Running the DTC

• | Ignition is in the RUN or ACC position.

• | System voltage is 9.5-15.5 volts.

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

### Conditions for Setting the DTC

• | The VCIM detects an open, short to ground or short to voltage in the cellular microphone signal circuit for greater than 10 seconds.

• | The VCIM detects an open/high resistance in the low reference circuit for greater than 10 seconds.

### Actions Taken When the DTC Sets

• | The OnStar® status LED turns red.

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

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

### 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.

#### 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 cellular microphone.
2. Test for less than 10 Ω between the low reference circuit terminal A and ground.

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

3. Ignition ON, test for 9.5-10.5 V between the signal circuit terminal B and ground.

⇒ | If less than the specified range, test the circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the VCIM.

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

4. If all circuit test normal, test or replace the cellular microphone.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Mobile Telephone Microphone Replacement

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