B2455

DTC B2455

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 provide an overview of each diagnostic category.

DTC Descriptor

DTC B2455 04
- Cellular Phone Microphone Circuit Malfunction Open Circuit

Diagnostic Fault Information






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 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 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(R) 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.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the cellular microphone.
2. Ignition OFF, disconnect the harness connector at the inside rearview mirror.
3. Ignition ON, test for 9.5-10.5 volts between the signal circuit terminal B and ground.

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

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

4. Test for test for 9.5-10.5 volts between the signal circuit terminal B and the drain circuit terminal A.

• If less than the specified range, test the drain circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the CIM.

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

Repair Instructions

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

* Mobile Telephone Microphone Replacement