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 04: Cellular Phone Microphone Circuit Malfunction Open Circuit

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Cellular Microphone Signal | B2455 04 | B2455 04 | B2455 04 | --
Cellular Microphone Low Reference | -- | B2455 04 | 1 | --
1. OnStar Microphone Inoperative - Caller Cannot Be Heard

### Circuit/System Description

The communication interface module (CIM) 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 CIM on the signal circuit. The CIM provides a ground for the microphone via the low reference circuit.

### 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 CIM detects an open, short to ground or short to voltage in the cellular microphone signal circuit for 10 seconds or greater.

• | The CIM detects an open/high resistance in the drain wire circuit for 10 seconds or greater.

### Actions Taken When the DTC Sets

• | The OnStar® status LED turns red.

• | The CIM 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.

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 CIM.

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

4. If all circuits test normal, replace the cellular microphone.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Mobile Telephone Microphone Replacement

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